BBT question

Brandi • My name is Brandi and my fiancé`s name is Joe. I`m 23 he`s 25. TTC baby #1. I`m a hair stylist and he`s in flooring.
How much does BBT change throughout the day? I took it this morning and it was 36.57 C and tonight it's at 36.97 C which seems like a big difference. This is my first month tracking BBT so I'm not really sure about anything. Please help!!