I am not pregnant but my period not caming?

Depends how late: It can be normal for a period to be late a couple of weeks due to stress.But it is important to rule our other medical reason such as a thyroid condition or other hormonal problems. If your periods is late by over 1 month, you should see a doctor for evaluatiom.

Amenorrhea: If irregular periods persist see a gyn doc for blood work to rule out any hormone abnormalities.

Possible Reasons: 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.