If the abdominal pain is accompanied with diarrhea and happens like first thing in the morning or soon after the breakfast, he may suffer from intestinal disorder, known as Irritable bowel syndrome.
If he has stomach pain (abdominal pain below the breast bone) that causes nausea, vomiting and eases after taking a food, he may have a duodenal ulcer (this type of ulcer activates after few hours of eating).
He may test his blood sugar levels, too.

Best wishes!
Marija