Cough from last 3 months. Major?

I was down with cough issue from last three months and meanwhile I visited to three different doctors. But nothing worked major. I had done my TB skin test and chest x ray test, both the reports were normal. Two week ago I visited one more doctor and told him about my cough issue, he gave me some medicine in three visits to him, following which I observed major improvement in my coughing but still I feel something like belgum or cough is stuck inside my throat. To clear this I have to cough. Is this is viral fever as all doc told me??? Or something major?? I don't know why is it happening to me from last three months. I am into depression because of this. It's very irritating. Please suggest me doctor what to do now. I am tired of taking medicines. (PS: In my previous visits to doctors I havent visited to pulmonologist yet. I visited to 2 MBBS, 1 BHMS and 1 general physician)