A little background info: I have PCOS & I had a transvaginal ultra sound a week before this happened and have/had a small cyst on my ovary. But my period was supposed to start last Tuesday but the Sunday and Monday before I had extremely light spotting. Then nothing until Thursday and it was extremely heavy bleeding with small clots. Usually a regular tampon will get me 6-8 hours, but in Thursday I was bleeding through a super in 2-3 hours. And then by Thursday night is had just stopped and nothing since then. My college nurse said possible implantation bleeding when I asked her Wednesday and she said to take a test. Well I've taken two and both were negative. Can anyone tell me what might be the cause?