I know what causes late or missed periods...Stress, severe weight change, etc....And of course pregnancy. It still seems strange to me that you can be late while on the pill, since it's being very controlled by hormones and such. If you're late on the pill, when do you usually get your period? In other words, how long should one wait it out before they get worried? Is it common to be a day late...Up to a week late? What?