could I be pregnant plan b only works so many times

So I have been in a relationship with my fiance for 6 and some years, I recently got back from work out of.state. So we had unprotected sex while I was on my period. My petiod had stopped it was very light pink and required no pad when we were done. It was not the first time he cam in me and i refused to take plan b because it would make me real sick, besides the pharmacist told me it could only work 2 or 3 times. Anyway its to early for me to tell whether I am or not, but is there chances that my intuition is correct even before a missed period. N is plan B the.only alternative there was I know birth control is what most of you will say but ive always been scared it will leave me sterile.