It looks like cysts of sorts, perhaps parasitic in nature, but again it is just picture. Hard to say, vet should offer you to do hystopathology, and/or possibly to do a culture, to see what is it exactly if he suspects bacteria. I wonder how old is a frog and if it had any contact with anything from outside, assuming it is cb. If it is in fact parasites ( most likely tapeworms) you most likely wont see it just like that by opening it, you need to do cytology on inside liquid and actually see their heads. They are too small to see without microscope.


amixacin is fine in a form you were using, but it is highly nephrotoxic, i would never suggest using for more then 10-14 days and only with sufficient fluid therapy ( water baths), that is why i suggested you stop using it, besides if antibiotics are working normally you will see it within 3-4 days, sometimes a week. If no better within this time frame it is indicator they are not working for your particular problem.


Yes hospital set up is wet paper towels on a bottom, that are changed every day, i would recommend to cover all 4 sides to minimize stress levels, put inside decor plastic plant to hide under, water bowl. Humidity, temp as usual.
I would also suggest to do a water bath with non flavoured pedyalyte and some diluted reptiboost. There is a specially formulated amphibian physiological solution that i use now, but it is a bit on expensive side to make and you need to order it through the vet, pedyalyte will work well too.
Have long had it been since he ate last?