BBT dropped 2 days after ovulation

Dee • Sat, May 20

My BBT dropped 2 days after ovulation and I don't know what this means. It's was 97.4 before ovulation then jumped to 97.9 and 97.8. I took my temp this morning and it was 97.4. I decided to take an OPK test this morning and it was positive. I'm so confused. Any thoughts? Thanks!