Delayed or irregular ovulation, caused by all the things mentioned above. The first half of your cycle (up to ovulation) can be of variable length. Not everyone ovulates like clockwork. Ovulation triggers the second half of your cycle, called the luteal phase. The luteal phase is typically between 12 and 16 days and that frame of time varies very little for an individual women (ie. all things being equal your luteal phase is apt to be the same length each cycle.) So in a long cycle, it's not that you ovulated on time and then stress 'delayed your period'- it's that something in the first half of your cycle delayed ovulation, and then you got a period after the usual luteal phase. Does that make sense?
I highly recommend the book Taking Charge of Your Fertility by Toni Weschler for demystifying the menstrual cycle- really good read, especially when ttc!
at 12:54 PM on Mar. 26, 2010