I have no medical expertise, only my own experience, so I'll stick to that. Maybe it will have some relevance.
I had what was diagnosed as IBS for years. It fitted the general descriptions etc. Finally I had one doctor decide to do a thorough check (ultrasound) rather than just accept the diagnosis. I was found to have many small gallstones. My gallbladder was ulcerated and I had apparently had the problem for some time. I had it removed and they collected and gave me and I kept the enormous number of gallstones. They didn't keep the gallbladder for me, shame! It was done via keyhole surgery. I had no idea that what I'd known as IBS was actually atypical gallstone symptoms.
I didn't have IBS now. Amazing.
Keep an open mind.