In a woman's cycle, ovulation is the thing that begins everything, then your endometrium builds up on case you got pregnant that month, then if you aren't pregnant, your period comes. Then when your body feels like it, it starts all over and ovulates again. Sometimes a woman is under stress, or has an ovarian cyst, or for some other reason doesn't ovulate in a given month. No ovulation, no entometrial buildup, no period to get rid of the endometrium. Skipping a period doesn't always mean pregnancy and it certainly doesn't always mean cancer. If your previous period was a bit weird or you have aches in your lower sides, it could be a cyst. If your next period doesn't come on around when you expect it, see your doc for an ultrasound.