Sounds like Dwarf Gourami Disease. One of the online sites I visited, from the UK, talks a lot about this disease and that Dwarf Gouramis are about 25% affected by it and it is due to poor breeding conditions in Asia where most are raised. They say it is pretty infectious and about 25% of the Dwarf Gouramis I've bought have had a similar condition. One had a sore on it's mouth that looked raw and another had a fin that looked almost as if it was swollen at the base and got more raw looking. Both died within days after this started showing. Supposedly, these fish are treated with antibiotics in the breeding tanks and by the time they are imported and the effects of the antibiotics are wearing off, they develop these symptoms.