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Weird hamster discharge? - hole above bum

My hamster has a scar on her belly, has not before two weeks, and I realized that last week, but decided to quit, but keep an eye on him. Then, before there was a kind of white "pus" only a small hole in the earth's crust, but especially her ass. Pus is a little stringy and sticky. Has anyone ever been to? Is to make it a worry? Is it better to (him to the vet and if it is expensive?)? Thank you, any help would be great.