How your cycle works
At the beginning of your cycle, one to two dozen eggs begin to ripen in each ovary. These eggs have a follicle casing that starts to produce estrogen. Like many things in nature, this becomes a case of "survival of the fittest" as the eggs compete to mature and be released. Enough estrogen must be produced to trigger the Luteinizing hormone, which allows the strongest egg to achieve its escape. This is ovulation. A very small percentage of women feel pain when this occurs.
The egg begins to travel down to the pelvic cavity. The follicle that once held the egg starts to release progesterone. This hormone prevents the release of other eggs, as well as triggers changes to your cervical fluid, uterine lining and the position of your cervix. If fertilization occurs, the body releases a hormone called Human Chronic Gonadotropin, which prevents the shedding of your uterine lining, otherwise known as menstruation.
Unless you are on hormonal birth control, the 28 day cycle – and more importantly – ovulation on day 14, is a myth perpetuated by the unreliable rhythm method and ignorant doctors. This misconception has been more detrimental than we'd like to think. It has lead to countless unintended pregnancies, years of struggle for loving couples trying to conceive, false accusations of unfaithfulness, and even rejection of medical coverage by insurance companies.
Follicular/Estrogenic phase: this phase starts on the first day of menstruation, continuing to the day of ovulation. It's length varies significantly from woman to woman.
Luteal/Progestational phase: starting from ovulation and continuing to the day before your next period. This phase usually lasts between 12-16 days.
Your entire cycle rests upon when you ovulate. Most women will have a pretty steady cycle, that is almost identical month to month. Having said that, many factors can effect when you ovulate, which will change how soon you get your period. Stress, travel, sleep deprivation, and exercise are just a few of these factors. Sometimes your body won't even release an egg, which too will change the behaviour of your cycle for that month.