Okay so my periods are usually normal sometimes there late a day or 2 but I get them every month I remember when I got my very first period it was the 17th of December , I had just turned 12 😭 ( this was a few years ago ) and they come around the same time every month but they have shifted cause I slowly started getting them from the middle of the month, the end , and the beginning , but it happens slowly , why does that happen ?