As one person said, not everyone ovulates at the same time. I took about 4 months of watching my ovulation before I actually tried to conceive - just to figure out my system. I ended up ovulating regularly on days 18/19. So, you may not have ovulated when you thought you were supposed to, but you could still ovulate. Now, on the flip side of that, I used a fertility doctor with both of my kids. The first one was conceived on day 19, but the 2nd fertility doctor (we moved to a new state) did NOT like conception on day 19. He forced conception on day 15 with drugs (which was fine with me because the result was still a baby). So, if you are ovulating that late, you might consider talking to a specialist about it. Our doctor indicated that an egg that matured that late was already "old" and wasn't a good recepticle for a baby (even though my son is fabulous!).
Also, be sure to use the stick first thing when you get up in the morning and be consistent about using it at the same time every day.
Good luck!
L.