Missed menstruation can be because of different factors. Stress, sudden weight-gain , hormonal imbalance, and reproductive system disorders can be listed as the most typical causes. Being aware of any other inconveniences that have appeared along with missed periods would help you to find out the real issue. It would be beneficial if you could communicate with a gynecologist in that respect so that the right diagnosis can be drawn without further delay, and, if needed, the best treatment would be provided to you.