A cold usually hangs around for 3-4 days, but I have a lingering cough that can take up to 3 months to go away. I'm a smoker, and have been prone to respiratory/sinus/throat infections since childhood (I was asthmatic until my late teens) so usually when I get a cold it turns into a chest infection, if it doesn't I still have a nasty cough.

Maybe pop into your GP to get it checked out and make sure it's nothing that needs antibiotics to get rid of?? Hope you feel better soon