What could case a delayed menstrual period aside from pregnancy?

Not ovulating: Many are stress related and have a delayed menstruation. If the problem persists, should see a gynecologist to have a proper evaluation. Chronic anovulation for a prolonged period of time is not a good thing and can increase risk of endometrial cancer. Some hereditory condition such as polycystic ovarian syndrome can have long history of chronic anovulation and irregular periods.

Delayed period: 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. #1 reason is pregnancy.