BBT ?!?

☆Heather June☆

Ok ladies I just went and bought a bbt thermometer.

It says to be like "half awake" to take temp. No talking no moving to smoking no drinks, take it right away first thing same time everytime (or very close)...

It also says to start taking it on first day of menses. Does it have to be or can I start doing it tomorrow morning when I do an opk? My opk says start day 16 and today is day 16. Thanks ladies