they are right that it is hard to diagnose something just be description, but it does sound pretty serious. like fish, amphibians are very sensitive to skin problems, which can allow pathogens and fungus into the body. they are also right that most likely a good vet will be your best bet to save the frogs life. unfortunately, even a lot of qualified exotics vets may not be able to do anything.
if you cant afford to take your $20 dollar frog to a vet and pay over $80 on its care (which is most likely the case) there may be a few things you can do.
one is to keep it clean and put it in quarantine, even if it lives alone. it would be easier to keep pathogens out of the open wounds if you had a simple paper towel or newspaper substrate which allows you to more closely monitor diet, feces and is alot easier to change out every day (which i also recomend)
i know most of the people on the board are not gonna be about this, but if its something life threataning and you cannot afford vetinary attention, you may not have much to loose from attemting to treat it with tropical fish, bird, or reptile medication available over the counter at a petstore.
i have seen some pretty severe respiratory infections, mouth rot, and other skin problems (like a serious case of red leg in a whites) succesfully treated with the broad- spectrum antibiotic tetracycline (often sold as "ornacycline) geared towards birds) usually a less than recomended dose would be applied to the water bowl or misting water (remember not to re-use the sprayer afterwords) and perhaps a slight increase in heat and vitamin supplementation.
i have seen this process cure a very seriouse case of red leg in a large whites, and some nasty cases of mouth rot were kept at bay in other herps in days.
this is just my personal experience and i dont know if it will or wont help your frog, and by all means dont do it if you dont think its a good idea.
the book "Care and Breeding of Popular Treefrogs" by Vosjoli, Mailloux and Ready is an exellent book with a chapter on treating various diseases of frogs.
it says similiar things to what iv told you, misting a diluted antibiotic solution once or twice a day.
i dunno, good luck with your frog and keep us posted
