first time BBT (advice please!)

L🌝🌸

Hi! I’ve been TTC #2 for a few months now and got AF today, I’ve been using opk and a fertility lubricant and have decided next cycle to track bbt! Firstly, probably a stupid question but where do you put it? Mouth, ear? I’ve seen online it also says vaginally 🤔 and does the temperature actually differ when ovulating? Thanks in advance xx