What is amenorrhea and what causes it?

You may want to consult an endocrinologist because you haven't got any periods at all. And that's actually rather different from having irregular periods. So broadly speaking, the reasons that cause amenorrhea, no menstrual cycle, is because the ovaries aren't working properly or because the ovaries aren't getting the signal to work properly, which comes from the pituitary gland located just below the brain. And if the pituitary isn't making the signal for normal menstrual cycle, then that needs to lead to evaluation of a pituitary status. And sorting out whether or not it's the ovaries that aren't working or whether it's the pituitary that's not working is something that's done through relatively straightforward endocrine tests.