HI. Thanks for your query and an elucidate history. You have posted the history as if you have read from the book : viz: The pain which starts in the upper abdomen and then shifts to the right lower side of the abdomen with or without fever or associated symptoms and now with rebound tenderness is to be taken as an attack of appendicitis unless proved otherwise. I would advise you to take him to the ER / Hospital Undertake blood , urine and ultrasonography. If proved to be appendicitis , go for surgery ASAP.