What might be some causes of a missed period besides pregnancy?

Hormone imbalance: Stress and hormone imbalance can be a major source of irregular periods, whether the stress is physical, emotional or psychological. There is a normal wide variation in the regularity of a woman's cycles. Please see your healthcare provider..

Here are some: Reasons for missed/late periods: low body weight, obesity, marked weight ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle (no egg released), travel, hormone irregularities, drug use, meds (i.e., birth control) or medical problems (i.e. PCOS). #1 reason is pregnancy.