Hi I can't offer any practical advise but I am presuming that the vet you saw was not an exotics vet? You can as the frogs owner ask that they consult with an experienced exotics vet. It is your right to do so if you are unsure or unhappy with the service you received. Manor Vet's (midlands) Manorvets Veterinary Practice 24 Hour Emergency and Critical Care West Midlands has an apparently decent exotics team, the tortoise trust has a list of vets by country, you can ring the practices and see if any vets have knowledge of amphibians. If they do get their name and find out if they would be happy to do a phone consult with your vet. To help get to the problem. I have done this before by pestering my vet to contact and exotic mammal vet to treat one of my guinea pigs, (yep even a guinea pig is apparently and exotic!)