I know I asked you before if your vet cleaned out the areas where the mouth rot is and whether he did a culture and sensativity test and you said he didn't....I should have posted again after that to say that usually if its not cleaned out properly it won't likely go away. If you don't have a test done you won't know if the antibiotic is the right one to kill the bacteria involved.
The most common bacteria involved with mouth rot is pseudomonas aeruginosa (sp?) and its not an easy one to get rid of.
Sorry that I didn't get back to your post to tell you that.