Back in my mid-to-late 20s, I used to have really bad intestinal pain, explosive diarrhea, constipation, all that mess. Pipes just weren't working right. Went to the doc several times, and they finally did a sigmoidoscopy - they said everything looked not only normal, but quite healthy. Had the barium test (yuck - like paint!) and it came back normal. Tried fiber, and it didn't work very well. They finally just called it IBS and waved good-bye to me.
A couple of years later, I went in to a chiropractor to see what he could do for a crick in my neck. For years, I had developed a distrust of chiropractors because my mom had back trouble, and every time she'd go see her chiropractor, she'd come out complaining just as bad as when she went in. So, with reservations, I went in to see a chiropractor my sister recommended - after all, who else is gonna fix a crick in my neck, right?
After an x-ray, the chiropractor starts checking out my back and asks me if I have any intestinal problems. Sorta shocked, I tell him yes. He adjusts my neck and lower back and tells me to come back in a few days. My neck felt better... but that wasn't the golden part...
...dude, my IBS symptoms vanished as if someone turned off a light switch. :Q
Turns out that when the nerves are pinched or blocked, you may not feel anything in your back... but it can still cause nerve impulses to not reach the organs they're supposed to communicate with.
So I went in as often as I could afford (at $25-30 a pop) to get everything straightened up once and for all... and to keep everything lined up as long as possible to help my muscles "remember" how my bones are supposed to be aligned. I now go every 4-6 months just to keep everything good, both with my neck and my intestines.
I'm not one of those people who thinks that everything can be solved by chiropractic, or that your particular situation would be helped by visiting a chiropractor. And there are plenty of bad chiropractors out there giving bad advice. But chiropractic certainly worked for my situation.
On another track... you might check food allergies. My brother is allergic to MSG (monosodium glutamate), so when he eats out, he has to be careful because he can have bad reactions to it. Since eating out exacerbates your problem, food allergies are worth checking out.