What can cause on and off belly pains that has lasted a few months and bright red blood in stool on and off in a child?

Many causes: There are many diferent cause of chronic abdominal pain in children, most common are constipation, acid reflux then there are less common reasons like ibd, celiac dis. Now bright red blood in stool means it's not coming frm his stomach at least it;s local. Better see your doctor to figure out.Family hx very important.

Intussusception: Intussusceptio9n is the telescoping of intestine within itself producing pain, lethargy and currant-jelly stools. One can also have a meckels diverticulum which is an outpouching of the intestine which can cause bleeding and/or intussusception. See you pediatrician, pediatric surgeon, or pediatric gastroenterologist.

Anal fissure/polyp: Anal fissure from constipation is most likely the cause and treated easily. Occasionally a child may have a juvenile polyp and it bleeds as it is trying to fall off. Would treat constipation first and if still occurs, see your doctor.