Since you have confirmed that you are not pregnant, it is quite certain that there is some sort of menstrual disorder at work. You have gone at least three months without a menstrual period - occasional and mild irregularities are usually nothing to worry about, but such a long period of time without menstruation does indicate that there is a problem.
There are a large number of factors that can cause a cessation of the menstrual cycle, so determining the cause is almost impossible without a thorough investigation. One factor that you need to consider is menopause - this usually begins between the ages of 45 and 55, but in some cases menopause can be premature, and can begin even before the age of 40. This itself can have several causes - premature menopause can be part of an autoimmune disorder or a genetic disorder, it can also be the result of strong medical treatment for a disease such as cancer, and it is also very common in women who have had a hysterectomy or a tubal ligation (sealing of the fallopian tubes).
Menstrual cycles can also stop as a result of sudden, drastic weight loss, or excessive exercise without adequate nutrition and rest. On the other hand, obesity or sudden weight gain can also affect the menstrual cycle. Stress is another factor that can affect the menstrual cycle when it gets out of hand. In addition, certain medical conditions are known to affect menstruation - these include disorders of the thyroid gland, polycystic ovary syndrome, and several disorders that affect the pituitary gland.
As you can see, the list goes on and on, and determining which of these factors could be at play in your case is impossible in such a forum. You should therefore make an appointment with your doctor, or preferably with a specialist, at the earliest possible time.
answered by M W