Frustrated with temping! 😩

About to give up on temping, not sure what I'm doing wrong. I started last cycle and noticed the thermometer seemed inaccurate, my temps were all over the place. So I bought a new, more expensive one for this cycle, but it seems like I'm having the same problem. Took my bbt this morning and my first reading registered really quickly so I took it again immediately. Got the second reading and decided to check the accuracy by taking one more time (again, I took it immediately after I read the second temp) I took all 3 without moving or sitting up. Here's the temps: 97.68, 97.93, 97.88. Kinda big differences for charting purposes. I'm wondering if it's my thermometer or if there's something about bbt I'm missing. Anyone been through this?