blood while fingering

i have never bled before during sexual activities, not even after losing my virginity. but a couple nights ago, my boyfriend was fingering me and his goal was to make me squirt (so he was going pretty rough), he pulled his fingers out and there was blood all over. later that night, i went to take a shower and my underwear were FILLED with blood. what could have been the cause of this ? did he accidentally cut me with his nails ?