Bleeding after sex

I finished my period yesterday so my boyfriend and I had sex the next day (today) and I started bleeding (spotting) again. I've heard the following from just a simple google search: sex restarts periods, we were too rough (which it wasn't that rough), not enough lubrication, I'm pregnant (???), left over period, etc etc. I'm kinda worried. Should I be freaking out or is this normal? Thanks!!