Cough for three months :(?

I have had this cough for about three months now. I get it really bad at night and sometimes in the morning. Through out the day, I cough every now and then. But in the first month, I was constantly coughing all day and night long. I went to the doctor right away because last year my cough got so bad that I had a sinus infection (I had nose congestion along with the cough, but not this time around) and the infection spread into my lungs. The doctor said they heard the flem or congestion in my lungs I think ? Well I was sick for about three months then and that sickness occured about the same time last year as it is this year. I was prescribed medication and my sickness went away fast. The first day I got this sickness, I was so beat down that I couldn't even get out of bed for a whole day. However, my only symptom was coughing. It was really bad for a week so I went to my doctor right away to prevent anything worse. She said she didnt hear anything in my lungs this time which i thought was weird because I am coughing up mucus. I was prescribed a medication for five days but I dont remember what it was. I got alot better, but it never 100% fully went away like last year. This cough gives me a tickle in my throat and sometimes I cough up mucus, and at other times it is really dry. I went back to the doctor about a month into my cough. She still couldnt hear any fluid and she put me on another 5 day medication and gave me Advair to use every 24 hours for about 24 trials(days) if i remember correctly. It helped alot, but still it is coming back and I feel like its getting worse again. The doctor did make me have x rays done on my chest to make sure I was fine and the results were fine. Robitussin helps, but nothing is making this go away. My whole life (15 years old) I have never had any chest problems or horrible coughing until last year. I do have spring allergies and I do have some reactions to dust, but never in the past have I coughed, just dry eyes and runny nose. Last year, my sickness was about january to march, and this year it started in the middle of april until now. I dont know what to do anymore :( someone please help! Thank you! Sorry for the long info, but I thought the more background info, the better chance someone can tell me whats wrong !