Filter air symptoms and conditions

My son age 3 was diagnosed with asthma about a year ago. Since then he has been sick constantly. Most recently his doctor has prescribed Singulair. He is aggressively pushing it on us. I stated my concerns to him, and he said there is nothing wrong with the drug.. he gets all the news letters.. and all the things I listed was the first time he heard anything.. I asked for his to refer us to a specialist and he wont.. I cant find anyone for a second opinion..My son needs medicine- at night i cant leave his side cause of his breathing.. The doctor wont suggest any alternate and I am stuck. I keep reading about all the people who are not taking singulair anymore- what what are they taking? I am completely lost here!