What might lead to missing a period?

Reasons: Reasons for missed or late periods can include: low body weight, obesity, marked weight gain or loss, over-exercise such as in endurance athletes, breast-feeding, stress, illness, eating disorders, travel, hormone irregularities, travel, drug use, medications (i.e., birth control) or medical problem(polycystic ovary syndrome or asherman’s syndrome. #1 reason for missed period is pregnancy.