I agree with the workup thus far.
Another consideration would be to further evaluate the upper GI tract. This can be done with an upper GI series or upper endoscopy, which can detect an ulcer, GERD, or inflammation of the esophgagus and stomach.
Other potential causes, if the tests remain negative, would be irritable bowel syndrome. But I would consider the upper endoscopy first before going in that direction.
A GI evaluation would not be unreasonable at this point.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin Pho, M.D.
KevinMD.com
Twitter.com/kevinmd