Hello dear I understand your concern Most common cause of absence of period for 3 months in sexually active women is pregnancy. Sometime if you have doe pregnancy tests earlier then it will give false negative result. I would suggest to consult gynecologist and undergo blood HCG test and USG scan to rule out pregnancy. In absence of pregnancy it could be due to Hormonal imbalance, ovulatory dysfunction, excessive stress, change in life style and dietary habit. You can ask gynecologist for progesterone tablet to induce period in absence of pregnancy. Avoid stress, take healthy diet, drink plenty of water and do regular exercise. Hope this may help you Best regards Dr. Sagar