Dogs and cats symptoms and conditions

My six year old son has been taking Singulair for almost three years for asthma and allergies. We have had such a hard time with him and it all started around the time he was prescribed this drug. He became very irritable, angry, hard to satisfy and generally unhappy. Now that he is six, the last two years have been the absolute worst with him saying he hates himself and just wants to die. He has stomach pain all the time and has had alternating daily diarrhea for over a year. Our pediatrician has done all sorts of tests and has referred us to a specialist. He has bad dreams every night and also complains of leg pain. He has been so depressed lately that he does not even want to go out and play after school and on weekends (not like him at all) and the teacher calls me several times a week to pick him up early because of stomach pain. I am so upset to think all this has been caused by this drug and he has suffered because of it! He also takes Zyrtec, as do all three of my sons, but the older two do not have asthma, just allergies. I gave him his last dose night before last because I just found out about the Singulair investigation. If anyone has any advice it would be greatly appreciated.