Period on the wrong days?

For the past few months I've been getting my period the week before its supposed to be due. I get my period in the middle of my third active pill week instead of during my placebo pill week. I thought it would go back to the placebo week after a month or so but it has been starting the same time every month still during the active pills. I used to start during the placebo week but then got off the pill for a while and started again. Will it ever go back to normal or is it just something that will happen?