My bbt chart this month

Lacey

I have a 13day luteal phase...My temp normally starts to drop towards coverline 12dpo and by 13dpo it falls under the coverline and the next day af is here,but this cycle at 12dpo my bbt went up and today at 13dpo my bb

t dropped but is still above coverline and hasnt fallen under coverline like it normally does.. what could that mean??