What Causes Vaginal Bleeding Post Nuvaring Withdrawal?

I had a cryosurgery done March 12, I have been off my birth control which was the Nuva ring two week prior to my procedure. I just had my monthly on March 30 and I now have unexplained bleeding like a period starting today. Is this normal after the procedure and is it normal for unexplained bleeding to happen being almost two month off the Nuva ring?