Previous Fertile Window Changed !?

Michelle • Married to love of my life & mother of 2 precious baby girls 💕🙏🏼

My last month's fertile window WAS originally beginning 2 days after the last day of my period and ended on Nov 23. Ovulation was Nov 24.

My period is 4 days late now.. and I checked my last month calendar and now the fertile window is way different ! Why would it change ??