Help! Whats going on? My af is due on the dot every 28days. Can plan for it! Last month and this month it's been 21days. The amount of days af is here remains the same, about 5-6 days.

Whats going on? Has this happened to anyone else? The only thing that has changed in my life at the moment is I now go for a walk every morning (except weekends! ) for anywhere between 30-60 mins. I've also lost 2kg since new years. Nothing else has changed.