My period is 7days late.what are the causes of late period?

Variable: A delayed period is usually related to hormone levels. Obviously, a common reason pregnancy. Hormone producing ovarian cysts, polycystic ovaries, thyroid dysfunction, stress, missed ovulation and various other issues may delay menses. This is usually not an issue if late menstrual period onset is a single event.

Late: 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.