Respiratory diseases can show up within 2 days to 2-3 weeks after a carrier comes into the flock. How long after exposure did you notice symptoms in your birds? Some common respiratory diseases are infectious bronchitis and ILT, both viruses, and MG and coryza which are bacterial. Antibiotics can treat symptoms of a bacterial illness, while viruses do not respond to antibiotics, but would run their course over several weeks. Look for bubbles or foam in the corner of one or both eyes, mucus from the beak or nostrils, gasping, sneeze or cough, rattly breathing, or wheezing are some symptoms that may occur. Sometimes the symptoms can help us identify a disease, and you can try to get testing. It sounds like infectious bronchitis or possibly, MG (mycoplasma gallisepticum.) Clean any eye drainage with saline or an eye wash. I would close your flock to birds coming in or going out of the flock, since your flock should be considered carriers. Here is a list of common diseases and symptoms:
https://edis.ifas.ufl.edu/publication/PS044#