PCOD is a major and very common cause of not having periods. This can very easily be dealt with medicines depending on the size of the first sin the ovaries. What was the size of the cyst in the ultrasound report? Thyroid can also be one of the reasons and can be confirmed by a thyroid profile blood test. I would advise you to consult a gynecologist for the first problem as it can very easily be managed by medicine. Rarely an operation is required for the cyst when it becomes large in size and this may also cause problem in conceiving in the future.