OPK Help

So I am currently 20 days late and I just got blood test results back and my HCG levels are less than 2 so I know that I am not pregnant. I have been using opk sine I was about 10 days late. I am not even close to a peak and my lines don’t have a progression of the darkness of the line. My opk I took last night tonight seems like it is lighter than the one I took the night before last night but tonight seems darker than the one from last night. Does anyone know what could be causing the line to be doing this?

The bottom test is from tonight