Unless one dies and you have it necropsied, there's no way to be 100% certain.What do you think it is?
And how do you know it's that, and not something else?
And what antibiotics would you recommend?
I don't have a vet that can prescribe anything.
but if it is a chronic issue, which by the symptoms, appears to be, you're going to get antibiotics here
https://jedds.com/collections/poultry-treatments-antibiotics