Theres something wrong with my goldfish, please help?

A yr n a half ago i got a goldfish f walmart. They said it was a fantail. I know its not bcuz it has a big round fat face. Not small n pointed like fantails do. Its all pearl white w a yellowish face. A couple days ago i noticed that its face had a few reddish colored blotches on it. Now 2day the blotches r all over its whole face. I have no idea whats wrong with it. I also have 3 shubunkins, 1 fantail, n 1 baby koi, that r in w it. None of them fight n none of the others r showing any signs of illness. The 1 w the blotches is acting n eating normal. But it dont look good at all. Does any1 know what this cud b? N how 2 treat it? If it is sick i dont want my other fish 2 get it.