I definately think it could be your gallbladder. I have been sick, just like you described, for over a year now. I've had all the tests you mentioned, including a hystorectomy for endometriosis, and still have had several bouts of n/v and pain. Recently I was diagnosed with gallbladder disease, a malfunction of the gallbladder which doesnt always produce stones. The Dr put me on flax seed oil to treat the symptoms, and perhaps bypass surgery all together. Its too soon to tell yet if this method is working. Keep up with the tests and checkups. You know your body better than anyone.