Implantation Dip?

Ar

Hi ladies,

I need some help. So typically I ovulate late and have a short luteal phase. This month I ovulated on September 25th (CD18) I am currently 5 dpo (my average luteal phase is 12 days) and I experienced a significant dip in my bbt (approximately .40). I went from 97.81 yesterday to 97.40.

Is this to soon for an implantation dip? Could it be something else?

Thanks so much for all your help in advance.