Help please !

Does sex cause your period to delay a couple of days ? Ok so me and my boyfriend are sexually active, we use protection with a condom every time. Two weeks ago it slipped up his thing, while doing it from behind, he pulled out and we stopped. I got paranoid and took plan B the next morning. My period is late by 3 days. Is there a reason my period is late. I don’t know if I could be pregnant because I’ve used protection every time and took plan B even when it was up to chance. Some help me please ! What should I do ?