Early bleeding on birth control-no longer effective?

I've been on the same birth control for a few years and my period has become quite regular. I'm diligent in taking the pill at the same time every night and have not missed a pill. I just started bleeding in the middle of my third week- I have three pills left before the last week of blue pills. Could the pill have stopped working? Do I need to use a back-up method of birth control?