Why am i bleeding again?

I've been on the pill for almost a year now. I started my period 2 days (I think it was a period) into the 3rd week of pills and I bleed for a week straight I had cramps and bright red bleeding. This hasn't happened before now I am on the 4th sugar pill and I am bleeding AGAIN not alot at all but I am cramping. I went to an urgent care about a week ago I got a pregnancy test it came back negative. They also took a blood test which came back negative. What could be going on?