There are several reasons why a woman have delayed menstruation and this could be due to unhealthy diet, stress (emotional or physical), sudden weight gain or loss, caffeine, alcohol
, and smoking. Gynecological conditions like polycystic ovarian syndrome (PCOS), and uterine cysts or polyps, can also bring about alteration in menstrual cycle. Even sickness and stress associated with it can delay periods. However, pregnancy is still the most common cause of delayed or missed period.