What Causes Bleeding After Masturbating Roughly?

Im a female 17, im also very skinny, so was my mother so I'm just under 100 pounds. I'm an extreamly rough mastorbator. I bleed heavy amounts sometimes. I never realy had a hymen to break, so I knew it wasn't that, also this is internal, I feel as though I proded my inner walls to hard and damaged them to cause the massive bleeding. I feel as though this is why I bleed so much. The bleeding can last a wile, but does stop after a wile. I just want to know if it really is because I'm going to hard...