We've gone through something similar twice - it definitely sucks because stomach pain can be so many things.
The first time with DD2, we thought it might be lactose intolerance, but it ended up being allergies, mainly to dust mites. She was swallowing a lot of mucus and that caused her stomach to hurt. Fortunately, she seems to be growing out of it now (diagnosed in kindergarten, growing out of it starting 5th grade or so).
When DD1 went through this recently, we had the gamut of tests. DD1 was/is taking a prescription antacid to help with the pain. There was some suspicion of celiac because it runs in the family, but when all the testing culminated in an endoscopy, that was totally clean for everything medical. She is now being treated for anxiety.
The advice we got from our pediatric allergist was NOT to remove any food groups unless you see an immediate/known reaction (e.g., throws up when he drinks milk - yes, then cut it out). This is so that they can keep getting maximum nutrition while they are not feeling well and probably not eating normal quantities. Also she said that blood tests for food allergies can be somewhat unreliable, and it takes considerable time to do the elimination tests properly. Celiac takes the biopsy for 100% certainty, as far as I understand it. It turned out to be good advice in both cases since neither DD turned out to be lactose or gluten intolerant.
Good luck with this. I know how frustrating it can be to go from doctor to doctor trying to get help.
Last edited by Ragana; 10-06-2014 at 10:30 AM.