Your Menstrual Cycle
Your period is part of your menstrual cycle, which starts on the first day of your period and ends on the first day of your next period. A normal menstrual cycle in teenagers is between 21 and 45 days. In the first and second years of your period, your cycle is irregular, and you may not have a period for some months. If you are underweight due to diet or exercise, if you are under a lot of stress, or if you are overweight, it can be difficult to predict your period. Keep a calendar and write down the day your period starts each month. This will help you predict your next period.
The menstrual cycle allows you to get pregnant. In the middle of your cycle, you ovulate, which means your ovaries have released an egg. You may have a few drops of blood coming out of your vagina when you ovulate. If you have sex on the day you ovulate or within 5 days of ovulation, you are more likely to get pregnant.