Periods...What's normal and what's not

Everyone's menstrual cycle is different.  They usually start between 9 and 14 years of age, they may last 21-45 days, most girls lose about 80ml of blood each cycle and many girls experience symptoms such as bloating, irritability, pimples and tiredness just before their cycle.
Some periods are not normal though and according to the www.womenshealth.gov you should see a doctor if:

• you haven't started your period by the age of 15
• your period suddenly stops for more than 90 days
• your cycle is shorter than 21 days or longer than 35 days
• you are bleeding for more than seven days
• you are bleeding so heavily that you need to use more than 1 pad or tampon every 1-2 hours
• you have severe pain during your period
• you feel sick and get a fever immediately after using tampons.