Have a test for anaemia as this can cause similar symptoms.
Hi, welcome to the forum, if one is not pregnant and there is absence of menses for more than 3 cycles or 6 months is known as secondary amenorrhea. The causes to be ruled out are hypothalamic dysfunction, Infiltrative lesions and Pituitary disease, Hyperprolactinemia, other sellar masses, Thyroid disease, ovarian disease, polycystic ovary syndrome, ovarian failure and uterine disease.
It is quite important to evaluate systematically. Thyroid disorder is also associated with amenorrhea and fatigue. Other symptoms of hypothyroidism are intolerance to cold and weight gain. Hence, evaluation with thyroid hormone, pituitary function, brain MRI, pelvic ultrasound will help to rule out the cause. Meantime you need to have nutritious food as well as measure of weight reduction, if you are over weight. Consult a gynecologist. Take care and regards.