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The hurting of stomach may be due to indigestion
and acidity as nowadays it is seen in children and also since it is associated with vomiting
.The main complaint that is not seen in children easily is headache so I would suggest you to visit a Paediatrician and get your son examined to rule out any signs of meningitis
if he has fever
along with headache and back ache.The doctor will examine and do the required treatment for him.