Yes, you have a discharge when you're pregnant because the mucus plug is forming at cervix. No, having sex on your period will not make your next one come late. If you're a teenager, possible that your cycles are not yet completely regular and that's why you could be late (if you are late, that is). If you are late and wondering/worrying that you could be pregnant, take a home pregnancy test...That's one way to find out!! Good luck