Orglethorp is right about temping alongside opk use. I didn't get a full positive in my opks with either pregnancy and rarely did the rest of the time either. It wasn't diluted pee or lack of testing since I kept bags of cheapies around and tested multiple times a day I just never got the test line to get equally dark but they got close.
In my original post, does cycle day8's test look as dark as yours get or did yours get even darker than that?
I have been slightly cramping yesterday and today so I took an opk yesterday morning with fmu and it was super light and took one today and it was definitely noticeable but not as dark as early in my cycle so I'm not sure what's happening! Haha