How late are you? The best thing to do is take a pregnancy test so you KNOW for sure it is not pregnancy related.

Anytime you have unprotected sex you could get pregnant. Use birth control and it makes your sex life so much better (no worries!).

Good luck!

I've always wondered about this. I'm not really sure if there's a medical explanation for it, by when I had sex the first time it threw off my schedule for a couple months. Same with a friend of mine. I'm not sure if it's common, but maybe it has something to do with your body adjusting to the releasing of hormones when you have sex, or maybe some kind of shock???

Anyways.... I say test, then you can relax a little

It has to do with fear and stress and the hormones released from that.