What Are The Side Effects Of Emergency Contraceptive Pills?

I was put on a lower dose birth control pill, because of headaches and I have been on that type of pill for months. This month I had my normal period which looked like it was going to end then it started over with really heavy bleeding. A new pad at least every 2 hours if not sooner with blood clots. I wanted to know if it could be from the new pill and if I should go back to my ortho-tri cyclen which never gave me these kind of problems, just headaches.