Hormones prepare your body each month for a possible pregnancy. The lining of the uterus becomes thicker with extra blood/tissue getting ready for an egg that moves down toward the uterus from an ovary. If the egg is not fertilized, pregnancy doesn't occur and the lining flows out of your vagina = menstrual period.

When you first start having your period, it may last only a few days and may be very light. You may only see a few spots of reddish brown blood. Anywhere from 2 to 7 days is normal.

The first day of bleeding in one month starts the menstrual cycle and lasts until the first day of bleeding in the next month. While a cycle can last between 21 to 45 days, the average menstrual cycle is about 28 days. Overall, it can take up to 6 years for your cycle to get regular.

Some girls have a cramping pain in the lower abdomen or back or breast tenderness just before and during their periods. Others get headaches or feel dizzy. Some get nausea or diarrhea.

On average, you lose 2 to 7 teaspoons of menstrual fluid while on your period. That might seem like a lot, especially when you're changing your period products. Menstrual fluid is actually a combination of blood and tissue from your uterine lining, which is also why you might notice clots or other textures that differ from a regular cut.It also depends on each girl. When you just started your period, it will be less.

Periods come in all different colors and textures — some are more red and liquidy, others may be brown and clumpy. Brown blood is just blood that’s a bit older. Some girls notice brown blood before they see red (on or before day 1), others have brown blood at the end of their period (day 5, or whenever your period ends).

Absolutely! You can do *anything* on your period—swim, dance, wear white pants, go camping, whatever — you may just want to use different period products depending on the activity.