My period's four days late. What's going on?

If there is sexual life under the premise, first of all to rule out the possibility of pregnancy. If it is not the cause of pregnancy, the general menstrual delay within a week is normal, there are many factors will cause menstrual delay, such as mental factors, environment, diet, etc. If more than a week menstruation has not come to belong to menstruation, to seek medical advice to do six tests of sex hormones.