Welcome to Sclero Forums. I'm sorry that you are experiencing some bowel issues. Please keep in mind that I'm not a doctor and have no medical training at all, and of course we can't provide any individual medical advice. But as I understand it, five days is not all that long. As I understand it, they only call it "severe constipation" when it lasts more than a week, and for some people it is normal to only go once a week. And of course, scleroderma can upset the intestinal apple cart for some people, and you should only use fiber supplements with the advice of your scleroderma doctor as they can worsen some motility issues.
That said, I do know how uncomfortable it is whenever we have any change from normal in our symptoms. It is good you are going to see your primary doctor tomorrow. If for any reason you do feel that it's a medical emergency, of course call or visit your local ER.
Altogether the intestines are about 25 feet long, so you can see it would take an AWFUL lot to fill it up to the brim! Therefore you should be on the safe side, and maybe knowing that little medical trivia, you can sleep a little better tonight.
Let us know how things go tomorrow, wil you?