levis lover

I recently quit smoking. I have been smoking 4-5 ciggs for the last 2 years. After quitting, i have been running almost everyday. I have been coughing up phlegm sometimes yellow, white and brown. But somedays when i don't run, i don't cough up brown phlegm. Only after running it is brown otherwise it is yellow or white. What should i do ? Should i see a doctor. It's been 12 days since i quit.