There's NO way I could be pregnant.... right?!?

Last time I had protected sex with a condom was the day before Easter. I got my period a week or so later so as far as I knew, I was fine. But my boyfriend said he heard from a friend that girls can get their next period but end up missing their next if they happen to get pregnant. That's not true right? How would the sperm even survive a period? My period is 2 days late and I've been nauseous for 4 days straight and anxious but I haven't actually vomited.