reassurance needed

Amy • Ig: wat_a_dazee sc:pinkypromiseamy
So last week i had sex with my boyfriend and for 3 rounds he came in me.( I have the arm implant birthcontrol btw 🤷🏽‍♀️) During sex my vagina started hurting due to his size lol
Well for the following two days, i had brown discharge and after i started bleeding like my period. So recap, 2days brown discharge & 3 days now of bleeding regularly.
I guess my question is; did i get my period because he left the cum inside or ir it because of rough sex??