Just took a measurement in my armpit. The temperature there is 0,2°C lower than the temperature in my mouth. Meaning that yesterday when my mouth's temperature was 37,2°C, that would be 37°C for your type of measurement (the same as you!).
It does vary. Body temperature measured orally, in the mouth, is 37C. Under the armpit is cooler at 36.5C since its external and up the anus (or vagina for the ladies who would rather measure it there) is a bit warmer, around 37.5C.