A 10-year-old boy has been having bellyaches for about 2 years. They occur at night as well as during the day. Occasionally, he vomits after the onset of pain. Occult blood has been found in his stool. His father also gets frequent stomachaches. The most likely diagnosis is
Peptic ulcer
Appendicitis
Meckel diverticulum
Intussusception
Pinworm infestation