Hello there,
Pregnancy is the commonest cause of missed periods. If pregnancy tests are negative other common causes of missed periods are stress, anxiety, eating disorders, too much of exercise etc.Hormonal imbalances, ovulation dysfunction and thyroid disorders are other conditions causing irregular delayed periods. Visiting a gynecologist and a clinical examination will be useful in determining the cause of your symptoms. Treatment will depend on the cause. Keep me posted.
Best wishes and regards!