regulating your period

crystal • ♡Artist♡music enthusiast♡cosmetologist💇🏽‍♀️
so my pd used to always come on the 20th, then it moved to the 19th for a couple months, once the 18th, then back to 10th, now it just started today on the 17th. why does it keep coming early? does this happen to others? and how do you regulate yours?