If you feel unhappy about menstruation, your feelings are perfectly normal. Try to remember that menstruation is a sign of maturity and health. You should also know that it will not last forever. Most women stop having their periods when they are in their late 40's and 50s. This is called menopause.
Many girls find it helpful to keep a diary of when they bleed each month.
Even if they are irregular, this helps them have some idea of when they might menstruate so they can prepare for it. You can buy a small calendar and mark with an x the day you start to bleed. Susan, aged 19, has a regular 28-day cycle. In April, she started to bleed on April 1st. So her next period started on April 29th.