Which one is right?

Sa
I've been taking my bbt orally for a while, and it's given me (what I think is) very accurate results. My doctor however is not convinced. He wants me to take my bbt every morning either in my armpit, vaginally or rectally. He says that taking your temp orally is not accurate (I don't know why).
But I'm confused. When I take my temp vaginally, it comes up as 99.7- way too high. When I take my temp in my armpit it comes out to 95.4- way too low. When I take my temp orally (using a different thermometer, of course), I comes out to 98.2- perfect.
Is my doctor crazy? Or am I just a nitwit? Which one do I use???