Actually I know quite a bit about periods. Haven't you noticed that most OBGYNs are male? Weight doesn't effect how early or late you get your period. If you are extremely underweight or malnourished, that can cause something called amonorrhea - which is when your period stops coming because your body doesn't have enough nutrients to "waste" blood on something like lining the uterus (body's more concerned about getting blood to the heart and brain). -J