Never got a positive ovulation test

So I started testing on the earliest day that I could have been fertile with the strips that are cheaper. They worked for my friend and I tested twice a day limiting my water intake submerging it for 3-7 second and checked it at three minutes but even waited the full 10 minutes. Not once was the test ever positive. There was one day were there was a super faded line but I wouldn't have thought that was positive....advice!?