Bleeding after sex ??

Jennifer • jëññŷçhïñ
Yesterday me and my bf were doing you know what. & we checked the condom afterwords and there was blood. Not a lot, or anything. But when I got home I looked at my underwear and there was a bit more. Ladies, if you have any idea what happened please let me know! Btw I am on birth control shot (depo), just if that has anything to go with it. Please help!