Pls help! Opk confusion

I just started using ovulation tests earlier this week since it's my fertile week. So far I've had no line or very very faint lines until today. I took a test on my lunch break at 12:20 and finally a line showed up. It was the darkest one I've had but only half of it was as dark as the control line so I decided to test again at 10 tonight. No line! Anyone go through this?