Hi Chesscab-
IMO, changes to meds including vitamins and supplements should be introduced one at a time. That way, problems with one or another would be more obvious.
I have to admit to being alarmed when I saw your age and the fact that you are on pred. IMHO, pred is prescribed way too much. It cures nothing and can cause serious issues in the future for users.
Have you looked into alternative ways to control UC?
I say this because I refused to take pred from the day I was diagnosed despite insistence from my first GI doc.
It took longer and meant that I had to accept diet and lifestyle changes, but now that's I have it under control, I don't regret making that decision.
Please consider alternatives to drugs with harmful side effects.
Many are discussed under the U.C. Resources tab.
My best wishes.
IAS