I keep coughing and it wont go away!?

I have been coughing for about a month now (mostly at night) and it truly wont go away and is beginning to really bug me!! I dont have a fever or runny nose so i know im not sick and this has never happened before. It doesn't hurt when i cough and its a dry cough (before i cough i feel an itch in my throat). My mother asked my doctor and she said it was just allergies but im not sure if thats what it is, My aunt says it could be asthma but my doctor has never said anything and symptoms of asthma have never showed up before and Im in track and have no problems with breathing. Can anyone tell me what it might be and how i can probably get rid of it??????? ps im 13