Singulair and uncontrollable rage

My son is six years old and been on Singulair for 2 weeks, on the 3rd day he started complaining of stomach pain. That night he had a horrible nightmare and everyday since it has been something else it seems to get worse everyday. Sleepwalking uncontrollable rage that we have never seen before. He gets out of breath very easy and his comprehention is very bad since he has takin this drug. He is on day two of no Singulair and is still having trouble sleeping but the other effects are slowly ending thank god any parents thinking of this treatment for their child needs to do more research my doctor did not think it was the meds that it is just a normal child stage he is going through. (bull-h--t).