double shifts?

I work as a caretaker for children with disabilities and I'm currently 28 weeks pregnant. I regularly work one 16 hour shift every two weeks because my job requires mandatory over time. It's rough, but I've managed. I called in sick this past weekend because all of the kids on our unit had a stomach bug that I ended up getting as well. Problem is, when you call off on a weekend day they require you to make it up. Anyway, this weekend is my Saturday to work my 16 hour shift and they made my makeup shift this Sunday, meaning I would be working 32 hours in two days back to back. I'm not sure if i am even physically capable of doing this nor do I know if I even should. I asked to make up my shift on a different day and was told no. Does anyone have any advice on what I could do?