Welcome to Sclero Forums. I'm very sorry you have such a family history of scleroderma, and that you have symptoms that are concerning to you.
Especially since you have been feeling particularly rough lately, it is a great idea to see your doctor. It sounds like you could use a good, old fashioned physical to better define some of your symptoms and to make sure that they are properly treated.
It would be appropriate to tell your doctor about your family history. Just bear in mind that with a family history of scleroderma, you are not necessarily doomed to develop it, even if your health history has been a lot like your mom's. That is because scleroderma is a rare disease, even in people who inherit a genetic predisposition for it; just because you might be susceptible to an illness, doesn't necessarily mean that you will develop it. They think with scleroderma that we must inherit some genes that make us prone to it, however they think something else has to happen -- perhaps an infection, or a major stress, or an environmental exposure or maybe a combination of things -- to make it actually kick in. (See Causes of Scleroderma)
Also, people with any close relatives with an autoimmune disease are more likely to harbor antibodies, without developing the illness(es), and they are also more likely to develop one or two symptoms of some (any) autoimmune disease without developing full-blown disease of any sort. Plus they have all the usual risk (like anyone else) of getting heart disease, cancer, diabetes which are often more life-threatening than any autoimmune symptoms (or disease) they may get.
For you, that is probably the good news and bad news all rolled in to one. What it boils down to is that it would be a great idea to develop as healthy of a lifestyle as you can manage. A well balanced diet, manageable activity, stress-reducing hobbies, and proper medical care might all help you avert the issues that your mother and grandmother have faced.
I may be wrong -- I often am, and you only have to read this forum long enough to see some real bloopers I've made! -- but from your exceptionally brief descriptions and my lack of an Internet Medical Degree (I paid my five bucks and ordered it, but it hasn't arrived yet), there are a couple of items I would no longer worry about, in regard to scleroderma, if I were you.
The first is that a scar-like thing on your arm is likely not scleroderma; it is most likely actually a scar. For some dumb odd reason, scars can show up when we get older or tanner, and they can grow along with us when we gain weight. I've had a few scars like that, which surprised me as they didn't seem to be caused by any recent injury, and that may be what you have found. (Or not, that's up to your doctor to decide, but this is just food for thought and hopefully info that may relieve some of your anxiety at the moment.)
And, the skin hardness of scleroderma, although some descriptions refer to it as being similar to scarring, is just not accurate. For systemic it typically begins with Raynaud's in the fingers (or toes) and then a very prominent swelling up like sausages of the fingers (called sclerodactyly), which makes it hard to bend the fingers. Later on, the fingers may begin to tighten and/or harden, eventually becoming frozen like a claw (if the disease manages to progress despite medical treatments.)
Fortunately, allergies -- even though yours sound like doozies and must be challenging to live with -- are just allergies and there is no particular relationship between allergies and scleroderma, that I am aware of, so far, at least. Allergies don't mean that our immune system is destroyed or that we will get scleroderma. What they mean is that, we have allergies and we must follow our doctor's advice on how to manage them, because allergies can be very serious stuff.
These "internal hemorrhoids" sound a bit worrisome to me. At least, enough of a worry that you should make sure you mention them to your doctor, and comply with any exam or tests they recommend to make very sure that the bleeding is really and truly due to hemorrhoids. It is very possible to have internal hemorrhoids but we should never assume that is the cause until we have been properly examined. I know those examinations are zero fun but think of it like this: having a baby is worse by any/every measure. But, to the best of my knowledge, no form of scleroderma causes rectal bleeding. (See Scleroderma Bowel Involvement) When scleroderma affects the colon, it usually causes constipation, sometimes diarrhea from bacterial overgrowth, sometimes intestinal pseudo-obstruction. Things like that. But not rectal bleeding, which can be caused by things like hemorrhoids, ulcerative colitis, Crohn's disease, and cancer. (See Causes of Rectal Bleeding by Mayo Clinic)
It would be very odd for scleroderma to cause sores on the chest. The type of sores scleroderma cause are typically limited to the hands, and are thus known as digital ulcers. Of course, by its very definition, digital ulcers wouldn't be appearing on the chest. But, a person might suspect those nasty allergies, once again, and you may need to have the sores examined by a board certified dermatologist since it sounds like they are chronic.
The sort of coughing that could be due to scleroderma would generally be one of two things. The first is that acid reflux (heartburn) which is very popular even among totally healthy people but which can also accompany scleroderma, can cause an intermittent cough. This type of cough would usually be after a big meal or after foods that cause you heartburn.
The other type of cough is the one that can accompany bad cases of pulmonary fibrosis, and it would typically not be a very intermittent thing because the damage is always there. Scarring from pulmonary fibrosis, especially if its bad enough to cause horrid coughing, would typically show up on your usual chest x-ray. May we assume this has been ruled out, when you were evaluated and ended up with inhalers? (Asthma might also go along with that whole allergy thing. Asthma can be fatal so be sure to always keep your inhalers handy and never ignore an attack, okay?)
Now we are down to the shins, and that's another thing for your doctor to evaluate. IF we can safely rule out the other stuff, then we can hope the shins have a less nefarious cause.
Then there is fatigue. I am so sorry you are suffering fatigue. Of course, scleroderma can cause fatigue but so can hundreds of other things, and scleroderma would be among the rarest possible causes. But there is something about fatigue that makes us feel like we have to be dying -- quickly, easily, soon! -- because it makes us feel like there is a horrible, deadly disease nipping at our heels. The question is, did the fatigue arise before you started putting everything together and wondering if it added up to scleroderma? Or after? That can make a big difference, because fatigue is a natural accompaniment to worry. The worry trashes our sleep so we have to sleep twice as long but we don't feel refreshed and just drag our weary butts from one minute to the next. It takes about five minutes to then be convinced we are on our deathbed.
If it's not due to worry, then you might be suffering from a virus, or a mild case of pneumonia, or whatever. All of this means that yes, you are right, it is time for you to see the doctor and get one of those head-to-toe checkups.
And personally, I'd recommend sticking around Sclero Forums, if you feel that it is a beneficial, positive experience for you (overall). Even if you end up being given the all-clear in regard to scleroderma, you still have some very real family issues to deal with. Feelings about your grandmother, concerns about your mother. Worries about your future. It is probably a good opportunity to make lemonade out of this experience. Learn more about the illness so you can provide knowledgeable support to your mother.
I hope I put enough concerns to rest that you won't be a basket case at your doctor's appointment, that you can have things sorted a bit different for priorities, and that you follow through with the tests as promptly as you can. It is good to figure out what's ailing you right now, as well as put the whole scleroderma experience (and just a vague worry about it is surely an experience!) in perspective.
Figure, if the absolute worst comes to the absolute worst, you still have us, and together we can all get through just about anything life tosses our way.