I've been temping for a long time and I've noticed - for me - my temps are way lower if I am in a deep sleep right before my temp time.
I don't sleep like a regular person lol - I typically fall asleep for only around 3 hrs a night - if that happens right before my 6am bbt then the temp is really low, before or after O... if it happens right when I go to bed & I am more awake before 6, my temp can be really high.
Now that I know this I can make a note & slight adjustment and my chart looks pretty standard. (I always have a "normal" 28 day cycle, O on cd14 - the most variation I've ever had is 27 day cycle!)
Anyways, maybe it's your sleeping pattern that's affecting your temps?