What the heck! 😦 Need help!

Ok so I found out I was pregnant on the 5th. The first test (far left) is from 9/5, the 2nd (middle) is from 9/12, the last test (far right) is from just now. Should I be worried that the line isn’t getting any darker?? Could there be a reason for that?? According to an apt on my phone I should be 6wks 4days, I have an appt on the 1st with obgyn. I’m just nervous!!! Aren’t your levels supposed to double everyday? If that’s true than the test today should be way darker right?