Hi, Elizabeth.
I'm 35 and also had a partial, then total thyroidectomy (TT) followed by 100 mCi of I-131 RAI, about 5 weeks following the TT. Other then the week off during surgery and taking the Friday off on the day of my RAI dose, I worked through it - however, I didn't work as many hours as I normally would (i.e. - normal for me is around 50 hrs week and I reduced hours to about 40 hrs week). That being said, after working through it, I wish I had just taken some time off during and after the RAI. I was very fatigued and brain fogged so it wasn't any fun working through that. Your case may be different though. For one thing, it sounds like you are going to take Cytomel up until 2 weeks before your RAI. I think that should keep you from going too hypo. I didn't take any replacement between the time of my surgery and the RAI so by the time I had RAI, I was really hypo. I was able to take synthroid 1 week after the RAI, and doubled up my doses for the first 5 days, but it still took about a month before I started feeling better. Someone else I know, who did take the Cytomel until 2 weeks prior to RAI, seemed to bounce back much more quickly than I.
I know you probably don't want to lose a semester, but perhaps, at a minimum, you can take a smaller courseload?
Good luck!