My 13 year old was put on Singulair 1 year ago for asthma/allergy...

My 13 year old was put on Singulair 1 year ago for asthma/allergys and it has helped tremendously with those symptoms. However, with the start of school several teachers have mentioned that he is often spacey, seems disinterested, non-responsive. He has also been extremely moody these past 6 months, angry alot, irritable, always tired. Since reading this site I took him off of the Singulair 3 days ago and his allergies have been horrific. I also started him on the Quercetin. Am wondering how long I should give the Quercetin to take affect? Anyone had experience with this? Also, should I stop the Singulair all at once or take him off slowly??