Often people don't realize how much hormone levels affect IBS. If the BC pills make it worse, this is an indication that these hormones are a bad idea for you. Nevermind what the doctor claims about the hormones and IBS, they often reach for the BC pills for other things that have nothing to do with prevention of pregnancy, too. As if messing around with women's hormone levels is such a wonderful idea! Also, there were some recent lawsuits over the Depo shots reported. And, Depo works on the same principle as the BC pills. Women were having all kinds of health problems with the Depo shots, many much more serious than IBS. And, IBS is definitely bad enough.
If you're feeling better without the BC pills, then by all means don't use the BC pills and go for alternate birth control methods.
I was diagnosed with IBS in 1998. I also found that when I was on birth control my symtoms were worse. Therefore I used other means of BC, however my doctor assured me that taking BC pill wouldn't affect it. I say do what makes you feel better.