Question about ovulation

This is my first month taking opks. I'm just curious will they be negative (only control line) until I'm actually ovulating or will will i start getting  a second line than starts to get darker coming closer to ovulation? I'm on cd 14 and been testing since the day after af ended and have only gotten one line. Glow says I Ovulate in 3 days. Just curious if I should be getting a faint second line or anything?