First month using OPK no positive test?

C

This is my 7th month TTC for our first baby and my first month using OPK strips.

Every month I get VERY obvious EWCM and so have assumed that I am ovulating every month.

This month is the first time I’ve used OPKs as I wanted to be sure that the prediction of my CM and the app were right and I’ve not had a positive test. I have had tests darker than others but nothing dark enough to class as positive. Any ideas what could be happening? I have a GP appointment in two weeks.