Singulair and od

My 14 year-od son was on Singulair for approx. two months. During that time he lost interest in activities he had enjoyed and seemed angry most of the time. He was constantly moving and was hard to communicate with because he seemed unable to focus. He also started having nightmares. I attributed these changes to puberty. However, I took him off Singulair about a week ago. Almost immediately his behavior changed. He is back to his old self. He is calmer, happier, more focused and enjoying activities again. Unfortunately, while he was on Singulair, he was nearly free of allergy symptoms for the first time since he was two years old. He has used Rhinocort, Clariton and Zyrtec. He is now back on Clariton.