Ovulation Predictor Kit---Line keeps getting fainter and fainter

Ashlyn
The first day of my last period was July 5th, and I have a 28 day cycle. I stopped taking my birth control this month. My husband I are now TTC.
I started taking ovulation tests on 7/14 in addition to checking cervical position, cervical mucus, etc daily. My peak day *should* have been 7/17. I have yet to get a positive result from the tests, but my test line got fainter and fainter as I approached what should have been my peak day and now it is almost nonexistent. 
I started using the equate brand early ovulation tests, and I figured maybe because they were so cheap thats why I wasnt getting a positive on my ovulation day, so I bought the ClearBlue digital tests and started using those on 7/16 and have gotten negatives every day since. 
Is it possible I didn't ovulate this month? Or did I maybe ovulate early and didn't test soon enough to catch my LH surge? I don't undestand why my test lines kept getting lighter and lighter as I approached what should have been my peak day.