Bbt in fertile week!! Someone please help!!!

Mrs.G

I test my bbt first thing every morning. The past couple morning's my bbt has began to rise along with starting my fertile week. But today on the second day of my fertile week my bbt has dipped down a whole degree but my opk clear blue digital says no lh surge. My bbt yesterday was 97.5 now this morning it was 96.8. What is the reason for this if my opk is saying I have not ovulated yet? Someone please help!!