bleed for maybe an hour should I still be worried?

I recently had sex with my boy friend with no protection. I don't have regular periods so I would have no clue when its late but the next day after we had sex I started my period, I think, but only bleed for maybe an hour if that. It wasn't heavy at all kinda a little spotty. I don't have any symptoms because this happened just recently and I know it takes a while for the egg to be fertilized. So my question is should I still be worried that I could be pregnant after this happened? Please help!