Hi. Most common cause of missing periods is pregnancy unless ruled out..you can confirm pregnancy by doing urinary pregnancy test.. In a normal menstrual cycle, a balance between the hormones estrogen and progesterone regulates the buildup of the lining of the uterus (endometrium), which is shed during menstruation. If a hormone imbalance occurs, mentrual irregularities occurs.. Periods can be delayed for a single cycle or it can be delayed in every cycle. If the delay is in only a single cycle, the most likely cause is a temporary cause like stress...Consult Gynecologist for further advice....