Hi Few women experience their periods at exactly the same time each month.Stress, change in routine and illness can affect cycle length in a given month. a late period combined with abdominal cramping may have several causes.a physical exam is the only way to determine the exact causes. but some causes are- Excessive weight loss or gain. Eating disorder such as anorexia. Increased exercise. Emotional Stress Illness Travel Medicines such as birth control methods Hormone Problem Problems with the pelvic organs,such as imperforate hymen,polycystic ovary syndrome. Breast feeding.