H.M.
If you have been sick latly or anything abnormal has gone on that could happen. Mine started coming early when I had a cyst on my overy. Just watch and keep track of when this one started and ends. And then if it comes in the right timing from when you started this time or if it goes back to normal time. If it is early more than 2 months in a row I would call your dr.
Good Luck and God Bless!