Talk to Gastroenterologist on Felling Pain In Stomach

sir, my son which is 8 years old now and often feels pain in his stomach before food and after food. many times i have received message from his school that your son often feel pain while he is in class. His weight is less than his averge weight. He is often avoid his food in breakfast, lunch and dinner. I already done his cbc and report was normal. doctor he recommended some iron and multi-vitamins. I already had given liquid medicin for pinworms. But still he always feels pain in his stomach.

i would be very thankful to you give me recommendation and medicine to cure this problem.