Basically you have secondary
amenorrhea or absence of periods/menstruation due to some thing. The first thing to check
for is pregnancy, which any case would be ruled out for you by now. Since pregnancy is not the case, then other causes will have to be looked into. Stress and anxiety is a major factor. Thyroid problems and abnormal levels of FSH, LH, prolactin, androgen hormones or male hormones and estrogen hormones too can be the cause.