My boyfriend and I were dry humping. I was in a thin polyester underwear and he was in cotton boxer underwears. He ejaculated whilst we were still grinding and I felt wet at the end. My underwear was was very thin fabric and moved around only leaving enough space to cover my vaginal opening.

I was also on the fourth day of my period. Is there a possibility that that some of his sperm could have gotten through the vaginal opening? And if so, could there be a possibility that I could get pregnant when I start my ovulation? I think the chances are very slim but im just very paranoid. Should I take Plan B as a precautionary measure?