It's impossible to predict the exact time, but your body will send signals that your first period is about to arrive. You may notice that your breasts are developing and pubic hair will start to grow. You will start to see hair under your arms.
You are getting close to your first period when you notice a discharge coming from your vagina. The discharge may look clear or white in color, and it may be slightly sticky or gooey. This is the time to be prepared by carrying a pad and an extra pair of undies in your purse or backpack.
Call home and have your mom pick you up as soon as possible. Remember every woman has periods and it's no big deal if someone knows that you had your first period.
During your menstrual period, your uterus contracts to help expel its lining. Hormone-like substances (prostaglandins) involved in pain and inflammation trigger the uterine muscle contractions. Higher levels of prostaglandins are associated with more-severe menstrual cramps.
Severe menstrual cramps may also be caused by fibroids, endometriosis or other conditions. It's advisable to consult a doctor when your cramps are very strong.