What Causes Daily Spotting And Bleeding With Cramps?

I am only 20 years old and have been on birth control for years. For the past year I have had a 72 day cycle. Recently I have noticed more spotting between periods and over the past week I have been having daily vaginal bleeding that is heavy for a couple of hours and then stops for about 24 hours. I also have cramps that feel like menstrual cramps daily as well, and experience cramps during sexual activity. My period is not due for another 3 weeks.