Has anyones temp dropped the day AF were to come and still got BFP?

Im 15DPO & my temp has dropped the past two days but no sign on AF yet. I thought I was gonna Start all day yesteday and last night. Nothing yet. My doctor told me not to even waste time to chart bc it will just add stress (which it obviously is ha). Just wondering if anyone has had their temp drop and still wind up preggo? Or is it pretty accurate that when ur temp drops AF will definitely show her ugly face?! A couple of my friends tried the charting and said it didn't work for them. Mine has been pretty accurate,,,,