Missed ovulation or anovulation?

Caroline
I've been TTC for 4 months now and this month I decided to start taking ovulation tests. I started in CD 12 since I have a 29 day cycle and it's been negative every single day. I'm now on CD 20 and I just don't think there's a point in taking any more. How do I know if I ovulated early and missed it or if I didn't ovulate at all??? I'm so frustrated!