I always have IBS symptoms when I have my period. I also often have my UC act up, many times causing to flare around the 4th or 5th day of my period. I take Yasmin birth control pills for packs in a row, so I only have my period every 12 weeks now. It works great and really helps keep my hormones in check. I've been doing it for so many years now I can't even remember how long.
Prednisone really screwed up my periods too, even on the pill. But reducing prednisone is what really screwed things up. It causes a hormone drop which often would make me get horrible cramps even when NOT having my period. So bad I had to take 1/2 Vicodine pill to get rid of it as they had me in tears and woke me up at night. Now that I'm down below 10mg of prednisone I don't get as much of an issue, I do see a little period-like spotting though each time I taper and sometimes get little cramps. Nothing as bad as tapering from the higher Pred doses though.