The temp drop could be a good thing, although it usually happens at about 9DPO. When you temp drops after O, usually around 9dpo, it is an implantation drop. But this could have happened to you for a couple reasons. Could be a little cooler in the house this morning or could have been a bad temp.
I'll be keeping my fingers crossed that your temps start going back up and hopefully you can get your P4 test done on Friday like you wanted and get an ovulation confirmation.