Has your period ever been late on letrozole?

I'm on my 3rd round of letrozole. The first 2 rounds, my period started right on time. Now I'm 3 days late, no sign of AF other than a little bit of cramping here and there, and pregnancy tests are negative. Ovulation was confirmed by my Dr. She told me if I still don't start my period or get a positive test today, to let her know.

Can a period be late on a letrozole cycle and having ovulation confirmed? I'm really confused right now