My son will be 6 in June. He has been on singulair since he was ...

My son will be 6 in June. He has been on singulair since he was 2. About a couple of months ago I noticed a change in his mood. Like he was depressed. Getting very upset if he couldn't do a certain thing. To the point of crying. Also crying if we get on him for something and not yelling at him just talking to him. He's always seems to be in a daze all of the time. And when you ask him a question, you sometimes have to ask him several times. To be 5 he is very hard on himself. He thinks he should be able to do anything and be good at it or he is very upset. He also thinks that everyone else is smarter than him when he is one of the smarter kids in his class. His teacher tells us. I feel he may of always been depressed but am just now seeing it, with him in school. Like many of the others, he has a hard time falling asleep unless its the weekend and we let him stay up later. He also at times has bad stomach aches, to the point hes crying. After reading some of the things people are going through, I'm going to stop giving him the singulair to see if his symptoms go away. Now I'm convinced that thats whats causing it.