Short Heavy Period What Could Explain A Short, Heavy Period?

What could explain a short, heavy period? - short heavy period

Normally I'm a light output that lasts 4 to 5 days. I can regularly or junior (SLIM-use), buffer for the duration of my tenure. In this month but my period only lasted 2 days and was so strong that I have gone through regular pads in a few hours and run into the store to buy hiking around. What could have caused this change? I am 21st I'm on birth control, but for a few years ago. Little has changed in my diet or exercise.