about your question i would like to tell you that constant hedache has many causes and simply we can reach the cause of your son hedache by some of simple steps.... common cause of headache is stress and anxiety and sleeping disorders and you should observe any emotional or psychological troubles your son has as it is common in this age...... second cause that is anemia and poor nutrition because anemia cause severe fatigue and headache and should be managed if present... third it may be brain vascularity disorder and you made ct scan so we can role out that if ct is normal... other common cause of hedache is visual disorders or photobia and my advice to you to refer to ophthalmology clinic to chech for any problems with eye.... at last you shouldnot get severe worry of that and just follow these simple steps wish you and your son happy life