Son (6 yrs) started claritin 3 months ago. since, hes now angry hyper and depressed. hes been off it for 3 days. when will it be cleared from his system? will his behavior return back to normal?

If is the claritin: that caused the symptoms to begin with, he would return to his normal self. It would take up to a week to be cleared of his system, if symptoms persist kindly have his doctor re-evaluate, chronic upper respiratory infection / middle ER infection can lead to similar symptoms, ENT evaluation may be needed, wish you both wellness