Your ovaries grow follicles and inside each one is a developing egg. When one gets ripe it is expelled from the follicle as ovulation. The egg travels down the fallopian tube and if it does not find sperm waiting for it and therefore doesn't get fertilized the egg travels into the uterus and is shed with the lining of the uterus which had been growing to make a nice place for the fertilized egg to burrow into. Therefore, your period comes from the shedding of the lining of the uterus not directly from ovulation.