Powell130- It really is amazing how important timing can be. Try to temp at the exact same time each day for a few days and let me know how things go.
The more precise you can be, the more correct your chart will be. What I have found works well is setting my alarm for a specific time and just going back to sleep after temping if I don't need to be up yet. I set mine for the very earliest I ever need to be up, so usually I do go back to sleep after temping. It works pretty well for me. GL!
PS: If you wake up before your alarm, but fall right back asleep, you can still take your temp at your alarm and it should be fine. Sometimes I wake up and hour or so before my alarm goes off because I have to pee. The short trip to the bathroom followed by going right back to sleep doesn't affect my temps. It does take a few hours for your temps to settle after first going to bed, but waking up for a few minutes does not usually raise your temp enough that you'll need three more hours for it to settle down. (Now if you woke up and ran laps around your house for a few minutes, that might be a different story!
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Edit: Some people also get flat temps if they temp orally due to mouth breathing. I don't know if that applies to you or not, but it is one of the reasons I chose to temp vaginally. When I started temping, I temped oral and my temps were not moving much at all. Turns out I breath through my mouth a lot when I'm asleep. (Just another thing to think about.)