My BBT dropped- am I out this month?

Frances

I am 7 DPO today, and 6 days from expected AF though I am not very regular. I had a post ovulation spike that stayed up for several days, but this morning my BBT dropped 0.6 from what it was yesterday. Does this usually mean that AF is coming? I've heard if an implantation dip, could it be that or is it too dramatic a drop? Any thoughts are appreciated.