He could of hit your cervix
This is my 3rd pregnancy and i usually bleed after sex while pregnant. U should be ok if it's light and it stop within a few min. Also, if there is no cramping. My cervix is just sensitive so i bleed. Good luck.
Kinda normal right after sex if it continues call just to be safe but there's a lot more blood flow down there so it's easy for him to hit one