Round 5, no O and 16 days late?

Katie 🌻 • 👼👼 👼👼👼
Has anyone else had this happen? I'm on round 4 of 100mg, and the last 4 cycles have been perfect. O on CD16 or 17, 30 day cycles. Then last month, no O (so no AF). Dr. prescribed Provera so I can continue treatments, but it seems strange to me that it would suddenly not work.