Could it be appendix problems? I would be very worried if it was that.
I had my gall bladder out about 3 years ago. I would have the attacks when I was riding (sitting trot) on my horse. The first time I had one, I thought I was having a heart attack and would die alone in the house (I'd crawled in, complete with my spurs still on). The pain was intense, lasting for about 1/2 hour. When it was gone, it was gone. This happened probably 4-5 times in a year, each time while riding my horse. I had my gall bladder ultrasounded also some upper GI barium tests. Turns out I had gallstones and they must have moved around or blocked a duct or something while I rode. I chose to have surgery. For me, it was not a bad deal at all. I was back riding my bike within 1 week and back on the horse in 2 weeks. The hardest was the stitch pulling on my belly button when I stood completely up (that's why cycling didn't bother it at all).
I hope you get some relief soon. Let us know.
Jeanette