What Causes Green Pus To Ooze From A Boil?

Hey there, I am a 19 year old male and I have a boil on my abs I got the black scab off and it is red and swollen and a little hard around the outside of it. It started off as just a little one now it has gotten bigger with green puss inside of it. I went to the doctor and he gave me some penicilin for it and I have been putting a warm compress on it as well as a bandaid with polysporn. Does the core have to come out and if so does it come out on its own I pulled a white chunk of something out of it. It has been with green puss for about 3 days now should I be worried?