May 2012 egd showed gastritis, colonscopy showed diverticulosis, .colicky diffused abdominal pain since dec 2012, could this be small bowel cancer?

Not likely: Small bowel cancer is very rare. It may show up on a ct scan or a small bowel series x-ray. Usually presents as painless anemia or bowel obstruction.

Not likely : Small bowel cancer is rare as my other colleague has mentioned. Chronic constipation is related to development of diverticulosis. Your symptoms may be related to chronic constipation and also you are at risk to have diverticulitis- which is inflammation of the diverticulosis ( pouching of the colonic wall). Those 2 could give diffuse colicly pain. You need to go to see your md for further eval.