Why am I still coughing up phlegm from quitting smoking?

Ok heres the deal. I started smoking at the age of 16 i am now 19 (almost 20), i quit smoking like 6/7 weeks ago and i am doing fine (no help whatsoever). I smoked packeted cigarettes for the first year or so then switched to roll ups. The number of cigarettes i would have in a day varied quite alot it could be anything between 5 and 20 (on a typical day it would be around 10). OK so i know from research for the first couple of weeks of qutting that it is completely normal to have quite a substancial amount of phlegm which is the lungs cleaning them selves of the harmful substances. 6/7 weeks onwards i still have ridiculous amounts of phlegm that does not seem to be getting any less. Any ideas why this is still happening?