Do you have anything else going on...even something that seems unrelated like migrains, bloating, or a rash, etc.???
I know this is going to sound crazy....but a few years ago my daughter was nauseous daily. Doctors ran numerous tests which showed nothing. When I was discussing this with one of her teachers she suggested I take her to a local chiropractor! I repeated that it was her stomach giving her the problems and she said that her infant Granddaughter had stomach problems and the hospital could not find the cause. They took her to the chiropractor and he adjusted her spine and she was fine. I took my daughter to the same Chiropractor and she was better after the first adjustment and only went for one more and she was back to normal! He explained to us that there are so many nerves from the spine going to all different parts of the body and that when the spine isn't properly aligned it can cause problems elsewhere.
I have gone to Chiropractors many times over the years but had never heard of going for a stomach problem. since then I have talked to others who have gone for constipation, migraines and other issues.
I wish I had more suggestions.....it might be worth a try if you know of a good chiropractor in your area.
Good luck!
Lynn:)