Sander different points under your tongue will give you different readings so as annoying as it is, stick with the first temp and try to stick to the same place under your tongue each day.
You could always try temping vaginally if there's a next cycle. Hopefully there won't be, but if there is then personally I have found it easier because there's less chance of it being incorrect or affected by things like having an open mouth in your sleep
Yes, this. I literally stick the thermometer in the same amount every morning, based on a ridge on the thermometer, take it, turn it off and go back to sleep. So easy. No fiddling about with making sure it's in the same spot in my mouth or having my lips closed the same amount, etc.
