Hi. Thanks for your query. Noted the history about your 15 year old son and understood your concerns. Pain in the abdomen needs to be seen by the Doctor for clinical evaluation, examination and investigations as needed. Please take him to the Doctor since the pain in for 3 days. He may need tests of blood, urine and stool and an ultrasonography to for the cause of pain in abdomen and headache. Headache with pain in abdomen indicate intestinal infection causing release of toxins that can cause headache, body ache and many other things. He would require a course of an antibiotic active against intestinal infection, metronidazole, probiotics; symptomatic treatment in the form of antispasmodic for pain in abdomen and painkillers for headache, electrolyte solutions and plenty of oral fluids to avoid dehydration and electrolyte imbalance.