Some vets have been known to treat reptiles as they were mammals. They adjust amounts and follow the same methods, the issue is reptiles have slower metabolism. Reptile vets often proscribe antibiotics for 3-6 weeks every 3 days.
How long was the antibiotic cycle? What was the antibiotic and was there a culture?
In my area there is a growing resistance to common reptile antibiotics. This has been made worse by incorrect antibiotic usage and mis use of disinfectants is also demonstrated to be a possibility.
Cultures are needed to target the correct most effective antibiotics, sadly if there was no culture done previously it takes many months for the antibiotics in the system to clear, cultures done with antibiotics in the system often are not very accurate. I would 100% suggest a culture be done if there was no attempt at a guess. After a incorrect guess a culture is not effective and a second guess might work.
If your vet guessed and or offered a short (week or two) antibiotic cycle I would look for a new vet.