What Is The Irregular Black Discharge?

Hi,
I have always had regular mensuration for 3-5days. 3days of heavy flow and some spotting on the 5th day. This time, for the first time, 9 days after I completed my periods, I am having blackish discharge. It started with yellowish discharge and turned into blackish now. The discharge is quite a lot and has been going on for about 2 days now. What could be the reason. Should I consult my gynea? please help.