super confused

Misheel
so last month i finished my period on the 20th and i became fertile on the 22nd. there is only a day in between. this months period i finished my period on the 17th and became fertile on the 23rd. why is there a 6 day difference for this month but only a day in between for last month??? i also had unprotected sex on the 23rd so im just completely freaking out