You have done pretty much what you can do. This sounds like a respiratory disease and there are many to learn about--Mycoplasma G., Infectious bronchitis (I.B.), and coryza are some of the common ones. Neucastles I believe is rare, but the others are more common. Some respiratory diseases can cause these other symptoms, so you might want to google "common respiratory diseases in chickens" and read a bit to find your chicken's symptoms. Many of these are chronic diseases and can come back, plus infect any new birds you get. These are viruses, so antibiotics like Tylan don't help unless there are secondary bacterial infections. Be careful not to spread what your sick bird has to your others although they may already have been exposed.