Cough that wont go away?

i had a really bad lung infection in september that i had antibiotics for and everything was fine after that but i began to have a cough again in early december and have had it for 2 and a bit weeks now and doest seem to be getting anybetter or have any signs of going. i seem also to be getting a cold which came on a few days ago but have been incresingly tored the hole time i have had the cough. is it just a bad cold or something else and what will make it go away as have tried many cough medicines and tablets but none work.