Then it is just likely to be normal irregularities in ovulation. Although we think of our cycle beginning on the first day of our period (like, the period leads to ovulation) the cycle actually begins with the day of ovulation (in other words, ovulation leads to the next period). For some people, there can be quite a wait between ovulations. (This is why stress affects periods -- a stressed woman might not ovulate, and no ovulation, no period.)
Yes, stress will do that, also at your age it is possible your ovulation is not entirely regular, and if you don't ovulate in a given month, you will not have a period the following two weeks. Is there any chance you could be pregnant?