confused once again

so i had unprotected sex about a week and three days ago. my period was three days early and my flow is really heavy. i'm currently on day three of my period. i counted the days from when my last period was which was 31 days ago but by any chance is there any possibility i can be pregnant ? i know it's not possible but two friends of mine just scared me saying i possibly can. i was feeling a little nauseous at work that's why they told me i can still possibly be pregnant?? sorry i'm just paranoid ! help haha