Things that can cause this are GERD, an ulcer, inflammation of the upper digestive tract, or pancreatic disease. The upper endoscopy is a pretty thorough test and can evaluate for most of these conditions.
Capsule endoscopy is typically used to evaluate the small bowel - it is uncommon for small bowel disease to present with left sided abdominal pain.
You can also consider an abdominal CT scan to further evaluate the pancreas or spleen.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
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, M.D.
http://www.straightfromthedoc.com