What is the reason for delaying menstruation for eight days?

Menstruation delay eight days first need to rule out the possibility of pregnancy, can use early pregnancy test paper for detection. If there is no pregnancy, may be related to endocrine disorders, lack of sleep, irregular work and rest, mental stress and other conditions may lead to endocrine disorders. There may be related to gynecological diseases, such as irregular menstruation, pelvic inflammatory disease and so on.