What Causes Prolonged Vaginal Bleeding With Blood Clots?

I am 51 years old. Up to the end of March, I have had my period regular and on time every 4 weeks. Pretty much like clockwork....I had not been to my gyno in a few years and decided to go the end of March. Doc asked if I had any problems and I said no...I got my period shortly after my visit and have not stopped bleeding since. I have very large blood clots that I need pads with the tampons. One day I changed litteraly every half hour. Is there any reason for concern? My pap came back fine.