Sex and bleeding

Tori

Ok so I had sex Friday with my boyfriend. No condom but he only came in my butt. He did penetrate vaginally but did not come there. When I got home I had bright red blood like I would be starting my period, which is due to start tomorrow. It wasn’t the same amount of blood that o have with my normal periods and it turned into spotting and then nothing. I know in my mind the implantation doesn’t happen that fast but just need reassurance!