Coughing up yellow mucous?

I've had a cold for the past week and a half, and although most of my symptoms are gone (feverish, cold sweats), I still can't get rid of constantly stuffed and runny nose, difficulty breathing, sore/raspy throat and voice, and the perpetual need to cough and hack up this yellow-with-a-shade of green mucous. Why can't I kick this?, what does the mucous mean, and what should I do that's cheap?