I have never had biofeedback done personally but I have heard good things about
it. From what I hear, its a technique that teaches you to learn your bodies signals and what its telling you. It makes you aware of your bodies reactions to stimuli and helps you to manage those responses.
I found this link http://www.aapb.org/i4a/pages/index.cfm?pageid=3368. It may explain it a bit better.
Psychotherapy has come a long way and recently within the past year have heard good things about hypnotherapy and IBS as well as cognitive behavior therapy and IBS. I personally would try the biofeedback, nothing to lose... wondering also if it may help with your migraines as well, might be something worth asking.