Abnormal behaviors symptoms and conditions

I have a 9yr that was placed on Singulair about 3 or 4 years ago with Concerta for ADD. He was always coughing at night and the doctor said it was allergies and told me to give him 5mg every night before bed. And the school said he had ADD. Well needless to say, my son weights 48 lbs and has had headaches. But he also doesn't act like a normal 9 yr old should. He does things destructively (breaks toys and destroys things in the house) and states that he doesn't know why he does things. He doesn't want to clean his room, shower, brush his teeth like he used too, and he acts depressed all the time. I ask he whats wrong and he says he doesn't know. He doesn't want to play outside or do anything remotely fun. After reading all these post I'm wondering if I should take him off the medication he's on and see what happens but I'm afraid of more side effects. The doctor says he needs to be on this medication. He has problems going to sleep at night is this a side effect? Any advice would greatly be appreciated.