Bleeding??? Need advice!

So I finished my period about three days ago. Yesterday my boyfriend and I had sex around 4pm. Long story short he finished inside me. I'm not on any type of birth control and we did not use a condom. Around 9pm after peeing I had very light spotting. I know it wasn't "leftover period" cause it was very light pink and only there when I wiped (sorry if it's TMI) has anyone else ever had this happen before? Or maybe knows what it could mean??