Bbt and ovulation

Nicole • Married June 2014, and TTC our first! :)
Few questions:
​Is it possible to get a pos OPK and not ovulate?
​Also, I got a pos OPK on cd 16, so glow put ovulation as cd17, but then this morning cd18, my temp continued to drop, is it possible I'm ovulating today and not yesterday? Or that I just didn't ovulate at all?
And this morning I woke up at like 7am, and took my temp, got 97.45 and then I happened to fall back asleep like immediately and took my temp again when I woke up the second time at about 8am and it was 98.20.  Why were they so completely different and which one do I use? I went with the first one since it was when first waking up..