Oh, yes, hormones definitely affect IBS. Hormones aren't just for the reproductive organs; they also run the entire body, including the intestinal tract.
Many women have had their IBS symptoms shift when they get pregnant or afterwards; sometimes IBS shows up for the first time after giving birth. Most all of the women on here have worse problems around their periods. Some birth control actually makes the symptoms worse at any any given time, while some types of BC seem to have no affect, or even make it better. What is good or bad, however, will largely depend on you (although several people switched to the Nova Ring--I think it's called--when they found that their pill BC was making their symptoms worse).