What Causes Prolonged Vaginal Bleeding While On Birth Control?

I been on birth control for 2 months and when I first took it I didn t have a period or breakthough bleeding until about 2 weeks later for a month than it stop than it came back this time for a month and a week. It s now brown string blood clots with no order. I take the pill everyday same time. Why won t the bleeding stop? First time on birth control does this mean it s the end? HELP ME!!