the information given by you seems incomplete , I think you should mention pain on which side and he has any habbits like alcoholic etc. as per your information probable causes are
Abdominal pain is caused by inflammation of an organ (for example,
appendicitis,
diverticulitis, colitis), by stretching or distention of an organ (for example, obstruction of the intestine, blockage of a bile duct by gallstones, swelling of the liver with hepatitis), or by loss of the supply of blood to an organ (for example,
ischemic colitis).
To complicate matters, however, abdominal pain also can occur without inflammation, distention or loss of blood supply. An important example of the latter is the
irritable bowel syndrome (IBS). It is not clear what causes the belly pain in IBS, but it is believed to be due either to abnormal contractions of the intestinal muscles (for example, spasm) or abnormally sensitive nerves within the intestines that give rise to painful sensations inappropriately (visceral hyper-sensitivity). This often is referred to as functional pain because no recognizable specific abnormality to account for the cause has been found - at least not yet.
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