Thank you for the query.
Usually in the abdominal X-ray
intestines obstruction in the upper level (like duodenum or first parts of the small intestine
) can not be visible. And his symptoms can point to that diagnose. Especially if the pain is located in the upper middle part of the abdomen, he have had the pain for some time now, has peptic ulcers history.
In such case, barium swallowing or upper GI endoscopy
would give the answer and this is the first test which should be performed.
He may also be suffering from gastroenterocolitis (if the symptoms has appeared recently) or food allergy
(especially if the symptoms do appear only after certain foods).
If the diarrhea
lasts longer than 48 hours, stool tests are necessary and proper antibiotic should be given (but obstruction needs to be ruled out first).
I suggest you to visit your doctor once again and discuss mentioned possibilities.
Hope this will help.