Okay ladies! So I have a question?

I was using the ovulation strips up until the 25th of March the pic below is how my stripped looked. (Pic with notebook)

Then after that on the 26,27 and today the 28 I got a negative on the digital clear blue one.

I decided to use a strip today after the digital one said negative and the pic where my nail is black is how it looks. I’m so confused?