The possible causes
for the pain
would depend on where it is.
Upper abdominal pain
can be caused by liver/gallbladder disease, GERD, or diseases on the upper digestive tract.
Lower abdominal pain can be caused by inflammatory bowel disease, irritable bowel disease, a mass, diverticulitis, appendicitis etc.
Depending on where the pain is, ensure that either an upper or lower endoscopy, as well as a CT scan and/or abdominal ultrasound is considered.