HELP!! OPK help please!!!!

Jessica • 9y.o daughter. 5y.o son. Trying for #3🌈baby

CD13- the past 3 days, I got a flashing smiley on Clearblue advanced OPK. Today I got a big fat empty circle. WTF?!?!? Why is this happening?!?!? I got my follicles looked at today and I had 1 dominate that was at 15. So what’s happening?!? Now I’m worried I’ll never ovulate. I’ve been using these for 4 months and this has never happened. Please help..