Taffy,
I’m not sure… If you had unprotected sex, then it is possible for conception to occur. Pregnancy tests won’t detect a pregnancy until a few days after implantation. Implantation usually doesn’t happen until about a week after conception so if there was a conception it wouldn’t have implanted in the uterus yet. It seems that if your period started that implantation would be less likely because of a thinner uterine lining from your period.
Honestly I wouldn’t worry too much. I would wait until your next period. If you are late then I would take a pregnancy test. For the future though if you do not want to get pregnant I would advise against having unprotected sex. Good luck and best wishes.
Kate