Depo Shot!

I got my first depo shot back in August I believe and got the second one in November. They said it might stop my period completely and that is what I was hoping for. But I have been bleeding everyday (lightly) for the past 3 months or so. I decided not to get another shot in hopes it would make my period go back to normal but I am still bleeding everyday even after missing the last shot!! Does anyone know why this is???