Fertile Window keeps changing!!!

Carolyn • Married for 3 years - TTC over 2 years for baby #1 #EndoWarrior
So today my fertile window was pushed back ONE WHOLE week. And my husband and I focused on the week BEFORE that for BD'ing. Does anyone know why it would have been moved by an entire week? And can this really be accurate? I'm sure my period will be next week... NOT in two weeks. Help!!!