Unfortunately, in the best interest of the snake, you're going to have to go back to a vet.

Oral medications for a snake are inferior to injectables, simply because they don't metabolize them the same way that mammals do. And since the Baytril (which is the brand name for enrofloxacin) is not working, I would recommend having them do a culture to determine the specific kind of bacteria so that you can get the correct medication to treat. If they don't know what you're talking about, you need to find a different vet. If you are really strapped for $$, you could skip the culture, but be aware that you might be wasting money on a different medicine.

I would ask them to start on Fortaz (ceftazidime) injectable. I don't know the exact dosage, but it's generally given every 3 days. We use Fortaz first for RI if the owner doesn't want to do a culture, and I'd say 9 times out of 10, it resolves the infection.

If you tell us what town you live in, some other members might know of a reptile vet near you.