Those symptoms could be caused viruses, which antibiotics do not work for, or by bacteria. There really is no way for you to be able to tell.
You'll need to make sure that if you choose to give antibiotics, that you follow instructions, including withdrawal time for eggs/meat that you may...
Probably just need to find an avian vet. They should be able to help you.
Even if they aren't as "up" on chicken medicine as compared to other birds, there are resources out there like VIN (Veterinary Information Network) that they can access to help them with the finer points of chicken...