Delayed response-2nd round clomid

Curious if others have had this experience with clomid and PCOS. I am on my second round of 50mg cycle day 5-9. Today I am on cycle day 15 and I had my labs & ultrasound done and I had a several smaller sized follicles and a large one in appropriate size. My doctor said the large one could be left over from my last cycle and will wait for my labs to come back to see if I ovulated or have not just yet.

Anyways, the RN called me an hour later for my labs and said that I have not ovulated just yet and to BD on the 22nd and 24th and to come back for labs and ultrasound on the 24th. Has anyone else had a similar experience using clomid? My first round, I took 50mg cycle day 5-9 and ovulated on cycle day 15.