It is somewhat unusual for a menstrual cycle to be only a couple of weeks in duration for most women. I recommend that you speak with your doctor
. The usual female cycle length is about 28 days, but can vary widely. It is especially variable for younger women, and can tend to regulate over time for many women. In addition to the obvious explanation of pregnancy, which can affect the female hormonal balance significantly and thus alter the menstrual cycle greatly, there are myriad other reasons for a cycle to vary. Weight is one of the most common factors, as being over or under weight can affect cycle length. Nutritional status and even stress levels can play a role, as can the amount of sleep that a person gets. Obviously, there are other explanations for menstrual bleeding
, and so if you feel that your period is coming on a very regular basis (such as you are describing), it is a good idea to discuss this with your doctor to determine if there is another explanation beyond normal variation. Some of the other things that can cause menstrual bleeding or irregular menstrual bleeding are serious, and require urgent medical attention. Please speak with your doctor about this question.