What Causes Heavy Vaginal Bleeding And Stomach Cramps After Starting Birth Control?

I am a 27 year old female who just started a birth control 17 days ago. on the second day I started spotting I now have been bleeding very HEAVILY and having PAINFUL cramping and huge clots for 10 days. I went to ER they said it should slow down but that was 5 days ago and I'm bleeding just as heavy now and my feet are swelling and my chest keeps getting tight. What could be happening?