Short cycle

My cycle this month has been ridiculous. I got my period on day 18 and my cycle is usually pretty long. Anyone have any idea why this is happening? I literally only had 11 days for a break from a period this month! I usually take progesterone to try and regulate my cycles because after going off birth control it took me 40 days to get a cycle so any Fred back would be welcome as to why my cycle is so irregular