Four year olds symptoms and conditions

My four old son has been on singulair for about two weeks. The change from wheezing/coughing attacks at night and terrible allergies during the day has been amazing. They are almost non-existent to this point a great plus. However, a i stress however his behavior and speech has been VERY INAPPROPRIATE and quite frankly it concerns me. He now states "im a bad boy" and "i dont listen" and his mornings are very testy to say the least. Granted these sound like normal 4 yr. old sayings that he would pick up from other children on the playground but how do you explain them happening almost simultaneously with his taking singulair. I find it very hard to believe that it is a coincidence and that these are normal things for a 4 yr old to say/do when all other things have remained the same. My advice is to diligently watch your child for these warning signs and find other remedies if you have reservations. Im not promoting natural cures but i am leaning toward a diet change for the whole family and consulting my doctor for food allergen testing. I hope this helps. Be Well.