Period late normally early?

Tiffany

Hi guys..... my periods are usually always consistent. They always Come 3-4 days earlier than the previous period so I always know when to expect it. I started on July 19 last month so I figured I'd start on august 16th. It is now the 21st and no period and no signs of one? This is odd for me.......... anyone have any advice on what may be happening?❤️