i have had to test several times till CD 17. it just depend on when you O and when you start testing. super sticky baby dust
It is possible to have your surge and not catch it on an opk. Not all Lh surges last that long. If you go to peeonastick.com, Elle shows a cycle called OPK Oddessy that has a Lh pase that would have been missed of didn't opk several times a day. I have had that happen, too. I usually opk 2x a day. Sometimes my urine is too diluted during the day to get a good result, also. Early evening is the best time for me or early am. Yes, I know they say don't opk w/fmu. But, sometimes that is the only time my will read. I drink too much H2o during the day :) BBT's back up the pos.
I am with Tina about the BBT, for me this is the best way to know anything. My LH surge is odd.... I can NEVER detect it with these 2 brands of tests... but with the Answer brand I can...
Now see, if I had never tried Answer and did not BBT, then I would think I was not ovulating....
BabyDust ; )