Singulair and 20 years old

My 4 yr old son has been on Singulair for 2 years now After having what was close to pneumonia, his pediatrician decided that we should try Singulair. He suffered from allergies all year round and both sides of the family also have a history of allergies. We went over the indicators to decide whether or not there was a good chance that he would develop asthma. Yes, we found there was a very good chance. We were told that Singulair is the one drug that could actually prevent him from developing asthma - so OF COURSE we said okay. He started so young, that we never really realized that this wasn't just his "personality" - you know terrible two's, then independence, then along came his baby sister...on and on. Anyway, he has always been an overly-emotional child, hyper, etc., but then it was like every little thing bothered him and he would throw fits about "nothing". One day I told him to stop acting this way and while crying he said he couldn't stop and asked me to help him to stop. How heartbreaking! He goes to preschool and can't sit in a circle for more than a couple of minutes without being reminded by the teacher to sit down. He has been especially aggressive - saying how he just wants to kick something or push his sister down. He has always been a restless sleeper, but just recently he has been telling me about his terrible dreams - things you would never expect to hear from a 4 yr old. I thought he was a hypochondriac b/c he was always complaining about something hurting. I was reading about ADHD and decided that maybe this was what he had - everything fit quite closely to these same behaviors. I called the pediatrician's office to see if this may be his diagnosis and instead they told me about the possibility that Singulair might be to blame. They told me take him off of it and see how things go. It has only been 3 days. I have not seen any improvement and his is very itchy and scratching like crazy. I'll let you know what we find out.