What Causes Productive Cough Along With Pain Under Breast?

Hi I have had a cold for about a month now. Finally the general symptoms have subsided and I just have a productive cough, and am still blowing my nose quite a bit. A couple of days ago I started to notice discomfort under my left breast and now it has moved up into my armpit. It feels a bit heavy when I breathe in/run. I also just started back to working out running/yoga on Sunday after being out of commission for a month. I am a smoker (4-5 a day) and had been on prednisone for th last week. Do I need to be concerned or is this just a side effect of my body getting back to physical activity or the cold?