My 15 Year Old Son Is Having Waves Of Intense

My 15 year old son is having waves of intense pain and tightness in the center right at the bottom of his ribcage. Made significantly worse by lying down. He did have the stomach flu on Monday with vomiting, but no diarrhea with it. He claims it has been off and on dull throughout the day, but got much worse about 30 minutes after eating this evening.