Oh boy, do I ever have IBS. My dad has Crohn's, has since he was 20 years old. He's now 61. His is severe, and he's completely disabled at this point, has been for about 15 years now. Because MY IBS is so severe, I have to get tested for Crohn's every 5 years for the rest of my life. Hey, could be worse, right? =)
My IBS is more the IBS-D variety. My mom has IBS-C, which I wish I could have much of the time.
Not sure what kind you've got going, or if it's the combo variety.
For me... keeping a healthier diet with fewer processed foods, extra water, and extra D (4k IU per day) definitely seems to help.
I have been treated by docs for mine, and we've determined that I am lactose sensitive (milk/cream bother me, as does ice cream, but butter, yogurt, cheeses, no biggie), and that I have absorption issues. I've been on several RX's for the symptoms but there's nothing that is safe to be on for extended periods of time, for me, that works.
I keep a steady supply of immodium in my purse at all times. 2 tabs does nothing for me - I take 4-6 depending on how bad my symptoms are, and typically I'll wind up taking between 4-10 of the pills per day when I'm really on a bad streak. I know, that's insane... but my body is NOT good with the intestines. =)
The only other thing that I've found works is medical marijuana, which is not to say use it to get high and act like an idiot. In my state, Fibro and severe IBS are both qualifying diseases to obtain your license, and I have to say that of all the "treatments" I've found, MJ is the only one that has relieved cramps, pain, nausea and the bleeding caused by my lower GI contracting too much. Not everybody agrees with the use of the plant for medicinal purposes, and if you're on that side, that's cool - I'd never push. But you might talk to your doc if your symptoms create bleeding or severe pain, which mine do.
If you're having major issues though, definitely head in and discuss with your GI doc. They'll probably have you do several food things, for 3-4 weeks at a time: No dairy, no carbonation, no wheat, no soy, etc., until they find things that seem to really set you off.
For me, iceberg lettuce is a major "no way" food", as is regular milk or large amounts of cream. And hey, fat-free froyo is yummy AND it's got fewer cals than regular f-f ice cream.