Peeling of skin in mouth after using mouthwash?

You have an hypersensitivity to something in the mouthwash. Sloughing of tissues (that is what you are describing) is a common reaction when someone has a sensitivity to a chemical in a mouthwash or toothpaste. It doesn't really have anything to do with your cavities. If the area feels raw try an analgesic mouth rinse and if the area does not heal in 2 weeks go and see a dentist or hygienist.