I dont want to frighten you or anything but the last time one of my friends had a persistent cough for 6 months it turned out to be cancer. He caught it early and got it treated.You should get it checked up with a doctor just in case.
Agreed. I did get a chest x-ray about 2 months after it started (and the rest of the cold symptoms had gone away), to see if there was anything there. Nothing found yet, but I am due for another check-in. This is a good reminder to do so :)