What Causes Vaginal Bleeding After Missing One Pill Of Microgynon?

hi i am currently on the pill mycrogynon and have been for 6 years now i missed one pill recently and now i am bleeding im worries as i normally bledd after missing 3 pills ( 3 days after when i have finished the pack) is this common i cant get in my doctors for 4 weeks ridiculous really what could it be i am not trying for a baby but could this be a case as i have read that you bleed when you are pregnant at first thank you