Has Vitex just STOPPED working for you?

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So I started taken vitex in June and got AF both in August and September so with this being my 3rd month on vitex I should have gotten AF again on Tuesday the 19th and it is now the 21st with no signs of AF coming at all so im worried that if im not pregnant then why didnt AF come? Did vitex jus stop working for me? Has this happen to anyone else?