So sorry that you're having such a rough time. I've been there. Here are some things that help me when the pain gets bad:
1) heat right on the abdomen (i use an old fashion heating pad right on my belly)
2) When I have a real gut wrenching attack, my doc prescribed a valium and a gabapentin (a pain reliever most often used for nerve pain). For some reason, these two will stop an full blown IBS attack in its tracks, usually within 30 minutes (from terrible pain to doing OK but goofy)
I do take Heather's acacia fiber twice a day, I take a pretty hefty probiotic (one that includes Bifido HN109), and have eliminated dairy and gluten from my diet as well as avoiding the usual triggers (seeds/nuts, raw fruits and veggies, artificial sweetners). This routine is boring as heck from a meal standpoint, but it's reduced my IBS attacks to one a month (from 2 a week!)
The other thing that really helped me (and I was extremely skeptical at the start), was the Hypnosis for IBS dvds. Don't know if they will help you, but when you're desperate like I was, you'll try anything.
I hope something here will help you. If you GP doesn't understand your IBS pain, find a GI specialist who does. It may take going to many docs, but it's worth it to find one that will work with you.
Best of luck!