I am 2 months late 4 period, sexually active. took pregnancy test 2 weeks ago, was neg. is the cause more likely stress? do i need to see dr for this?

Possible Reasons for: Missed periods: v body weight, obesity, marked weight ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle, travel, hormone irregularities, drug use, meds (i.e., birth control) or medical problems. #1 reason is pregnancy. If no period x 3 mo's s then it would be important to see dr (or before for other sxs).