Fished Clomid, Ovulated, No AF, Negative PG Test

Maddie
So I finished my third round of Clomid I am about 15 or 16DPO. No period with negative pregnancy tests. I got a positive OPK CD19. My first two rounds of Clomid I also got a positive CD19 & my period came about 14DPO. 
WHY is AF not showing up this time? I don't think I'm pregnant - especially since the tests are negative.
Could I have really not ovulated this round & the positive OPK was wrong? I used Clearblue & they've been accurate for me previously. 
Any ideas would be helpful. I'm calling my doctor tomorrow if AF still hasn't shown, but I've been worried all weekend! 
Thanks ladies!