Suggest Treatment For Itchy, Rashes On Hands

Hello, about a month ago I broke out in a rash across my ring and middle fingers on both hands. It is very itchy, and has small red bumps, some become blisters. It is spreading to my upper hands now. I have not been exposed to poison oak or ivy. I can't seem to cure it with cortisone cream, any suggestions? It's getting worse and now I have a small patch on my ankle. Thank you!