What Causes Earlier Periods?

Hi Doctors, i don't know if i should call this sex but i my boyfriend and i had sex unprotected sex for about 5-8 minutes but he didn't ejaculate anyhow about 5 and a half hour later i took the Postinor2 pill...i didn't have any side effect or anything...i was expecting my period on the 20 of June but it came on the 11th...now i'm feeling upset most of the time.. could i be pregnant?