Environmental sources symptoms and conditions

My son requires two forms of medications to stop the running nose, singulair and pediox. The two together were a very good combination and it did work. By eliminating the signulair on Oct. 6th, his nose is already running and he is coughing. We have tried Zyrtek and a few others I can't even remember, but none work as well. If anyone has any suggestions, please let me know. I will be calling his pediatrician for other suggestions, but I know she will be against us taking him off of the singulair, especially since he has had pneumonia in the past.