Kitkat is right. I'll only add that it is minutely possible to become pregnant while still on your period. If you have a very short cycle you could ovulate within a few days of your period stopping. And since sperm can survive for up to 5 days inside you, it is possible to have sex while on your period and still get pregnant. I hope this answered your question.
No, because ovulation has already occurred. You cannot menstruate (apart from those who have a rare anovulatory cycle) without ovulating. Ovulation determines when you're going to have you period.