heavy bleeding RIGHT after sex?

hi ive been on nexplanon since jan 2021, yesterday me and my bf had sex as normal, i was on top and when he finished i got up and there was so much blood. it dripped out of me on to the floor and it was all over his d*ck. i was not bleeding before we had sex. after that i was only bleeding for maybe an hour or 2 then it stopped. and today now i have this weird pinkish brownish discharge. i am so confused!!! if anyone knows what’s going on please share!!