I had about 15 mouth ulcers a week ago. They are gone now but the inside of my mouth is peeling and I don't know why?

Healing. You could have had a virus that caused the ulcerations. If they were large enough then as they heal the dead tissue will slough away. This should resolve on its own. The peeling could also be unrelated and can be caused by an allergic reaction to something such as a new tooth paste or mouthwash. If you recently started using a new product then discontinue its use to see if the condition improves.