Sore Lungs?

I am a 28 yr old male who quit smoking 6 months ago after 12 years of steady 1 pack a day intake. I quit because I had a persistant feeling that I could not breath properly, especially at night while lying on my back. I went through the typical period of hacking up phlegm, wich stopped about 4 months ago. Although I feel that I can breath much better than before, my lungs still have a "sore" feeling much of the time, especially after I do cardio excercise (i run for a half hour 3 times a week). I still have a mild cough, wich is only a little productive. I now also find that if I am around smokers or if take a few hits off a joint that drawing air into my lungs is quite difficult, and in addition to the "sore" sensation I feel that I cannot completely fill my lungs. I would see a doctor to get checked out but like many hard working freelancers I do not have health insurance. Anyone have an idea about what this may mean ?