I grew up with a "nervous stomach" as a kid and was formally diagnosed with IBS as an adult. Mine is definitely stress-related.
Here's what helped me: First, the one thing that really helped me start getting it under control was using Metamucil daily--a friend of mine who also has IBS told me about it and it absolutely saved my life at the time--I was at the point where my symptoms were so bad it was hard to get work done at the office. The fiber powder--not the capsules--somehow kicked my GI system back onto an even keel. I used it daily for a few years, but now only go back to it when I get a flare-up, which happens mainly when I'm under extreme pressure at work.
Second, exercise: When I was first diagnosed in my 20s, I did workout (I ice skated 5 days/week)

. That helped some, but it wasn't until I got into heavy duty cardio in my 30s that I found that it controlled my IBS. I racewalk about 5 miles a day--it really keeps things under control, esp on days when things are going nuts at work and my stomach is reacting.
Third, unfortunately, time: Ugh, I know this isn't particularly helpful to say to you, but it has gotten better with age for me. Maybe I'm learnign to deal with stress better? If so and if your IBS is stress-related, then maybe a program that teaches you to cope better with stress will help--meditation or yoga, perhaps? It might be worth a shot.

I did once hear about biofeedback programs for IBS, too.
I haven't tried the new meds that are out there for IBS--for me personally it's not worth the potential side effects, but that's just a decision that is right for my individual circumstances.
Hope this helps--keep trying to find something that works for you!