Singulair and Stuttering

We are currently waiting on the results of allergy tests for our 3 1/2 year old son. He has been on Singulair for six weeks because the doctors suspect that he does have allergies. I have noticed a definite change in aggression and not listening as well. Recently though, he has started stuttering. I was wondering if anyone else has had this effect. He went through a small bout of stuttering when he was 2 but it cleared up within a few months. His brain was just working faster than his mouth. He is extremely verbal. I have a suspicion that the singulair is causing it this time. I'd appreciate your input.