Chin with labored breathing, not getting better with antibiotics. Thoughts?

I have a male chinchilla named Malfoy who is around 9 years old. Back in December, he started getting a white discharge in the corner of one of his eyes, and then the other eye as well. He then started to have labored breathing and congestion, so I took him to an exotic vet. The vet said his lungs sounded good and thought it might be an upper respiratory infection. For the next 10 days I gave him an antibiotic and eye drops, and he got much better. Had a followup vet appointment and...

Chin with labored breathing, not getting better with antibiotics. Thoughts?