BBT help!

Francesca • I`m 31 and We just had our 3rd baby! A boy after two girls! Lots of losses 😔 my first arrived at 28 weeks, after five years of trying, our second arrived at 34 weeks, and our third arrived at 34 weeks too! So blessed!
Does anyone else do this? I bought a thermometer that does it properly and took it yesterday but forgot today before I stood up! Does it absolutely have to be as you wake up after a three hour straight sleep? My daughter still wakes up a lot in the night so three hours beforehand in never guaranteed! Any advice?