ovulation tests

so this month I decided to do ovulation tests as taking the laid back approach hasn't worked for us..ive been taking them for the past 2 weeks and haven't had a positive yet, had a very close to posotive a week ago but still wasn't as dark as the control line, I'm currently cycle day 28, is it possible that I've missed my ovulation as I tested too late in the day or any other reason that could be behind it?? don't know if I should be worried that I'm not actually ovulating ... any advice would be appreciated x