Please help? Confused?

okay i've been on yasmin for a few months, switching on and off cuz i miss too many pills sometimes but im taking it for my acne so it doesnt matter. but anyways i have about a weeks left of pills and it seems like im going to start my period early. i missed twice this month but i took 2 on one day and two the next day to catch up. so idk why im spot bleeding sort of?