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.