Not all vets stock Fortaz since it has a short life expectancy. Apparently there is a shortage with the online sellers as well, so even if you do have a prescription you may not be able to find it.
OP if you have a privately owned compounding pharmacy near you try them - assuming you have a prescription for it.
My vet just gave us an entire thing of it. We are treating our bearded dragon once every 72 hours for 6 weeks. She told us to keep the rest incase we need it for our snakes - she said it's good for a year.
Not sure if you saw a vet or had a culture done but I personally would not feel comfortable just throwing antibiotics at my reptiles as the stuff is rough on them to start with and you aren't even sure if it will work or work well. You could end up creating a resistant bacteria assuming the problem is bacterial and not fungal or viral.
And at the risk of being rude, if you cant afford to take an animal to the vet, don't get or keep said animal.
With that said, good luck on whatever you plan to do.
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