Hey. My Name Is Michaela And I'm 18. Last Night

Hey. My name is michaela And I'm 18. Last night a little incident happened and I'm worried. So I'm on the birth control pill. I don't have a period until i have to. Last night i was having sex with my partner and when we finished, i noticed i was bleeding and pretty heavy to. I wasn't bleeding before the sex and that isn't my first time having sex. What should i do about this?