Why am I getting a lighter pregnancy test?

Chloe • 👶🏼 👶🏼💙🌈 22🦄
So my partners told me to take another test just to see if it's darker then the first but it's not! Why is it lighter? I'm supposed to be 6wks +4 and I also have real bad lower back pain but only on one side. What does this mean with the tests being lighter and the pains?