Hymen separation is the usual reason for bleeding after the first sex. This is usually a very tiny small amount of bleeding from the vagina. And yeah, your period might have started a little earlier just from having sex.
Finally, it's not very likely, but if it's very painful, it's possible you could have torn your frenulum clitoridis. This would be very painful and bleed from under the clitoral hood.
How can you be so sure its not your period??? Is it heavy bleeding?? Dont dismiss your period so easily… penetration can kick-start your period, even when your period is not expected…
Heavy bleeding can also be a miscariage… Probably your period.
Hi Tiddly, First I hope your guy had a condom on or you are on the pill, could be if it was your first time, could be your hymen broke, and its just taken a longer to heal,
come back if its not that.
Good Luck