Initial damage symptoms and conditions

My 6 year old son has been on Singulair for 2 years and I have noticed a big change in his behavior but it all started with leg cramps and falling down alot..I told my dr about what was going on but she told me that it was nothing to worry about that it is growing pains..Before he started the on the singulair he was always a happy go lucky kid never had problems with him back talking or ever really getting angry. Now that I read all these reports these are the problems I have with him now:
My child has never offered to hit, kick or slap me but in the past year he has gotten more aggressive not only toward me but others as well..
He is fearful of people now thinking that they are being mean to him or picking him out to pick on or make fun of.
He has problems of headaches on a regular basis but just thought it was due to his sinus infections...
I have also noticed that my child has started hurting himself like punching even slapping himself in the face when he gets really angery or fustrated about things..
Sometimes he has problems with nightmares but not that much..
He also has problems with stomach pain as well...
My concern is taking my son off Singulair with his asthma being under control right now and he just recently had sinus surgery but I think it will be the best thing for him just because I want my sweet child back not the aggressive and abusive child he is now.... That is why first thing in the morning he will be taking him to his dr to find another medication to put him on and take him off the Singulair....