Flat BBT

Jacki
I bought the purple Rite Aid BBT thermometer last week at the start of my cycle. I have had a flat reading of 97.70 for 7 days now, which seems kinda wonky. I've checked my temp at other times in the day to make sure it works, and I get other, higher temps then. Is my thermometer wonky in the am, or could I just be that consistent?