The menstrual cycle is a very natural cycle that occurs when the egg that is released has not become fertilized. During the fetal stage of development the female produces about 400,000 potential eggs. These eggs play an important role in the menstrual cycle that occurs each month. When the egg that is released does not get fertilized it will not adhere to the uterine wall and start development. The days are counted from the first day of bleeding to the day before the next period.
Ovulation occurs at midcycle.
The point when we have a bloody discharge is when the endometrium sloughs off and is discharged. If fertilization occurs, then the endometrium is maintained for the embryo to implant and grow in. The pain that may accompany your period is usually called cramps. Prostaglandins are hormones that are released from the endometrium and cause the contractions of uterine muscles which may result in a cramping sensation. Some symptoms are bloating, breast changes, headache and fluid retention .