I would like to know your previous menstrual cycle pattern..It's nothing related to your rubella vaccine..so forget about it at present..cerazette medicine is a progesterone ie, hormone..so taking it, may cause hormonal imbalance..so irregular periods may occur with it, sometimes very less bleeding also may occur..if
pregnancy test is negative, it's better you go for TV sonography to know endometrial lining and ovarian follicular status.. correlating of these findings may help us to come to the diagnosis