There are other respiratory diseases that have telltale markers that identify what disease it could be, Here they are:
Infectious Bronchitis (IB) is a virus. It spreads through a flock quickly, hens lay wrinkled eggs. There isnt any treatment since it's a virus.
Coryza. Facial swelling and a very noticeable foul odor around the head area. Treatment is a sulfa drug along with Tylan or Baytril.
Mycoplasma Gallisepticum (MG). Bubbles in the eye(s), droopy eye(s). Treatment is Tylan, Baytril or Tiamulin.
Infectious Laryngotracheitis (ILT). Coughing up blood or slinging blood from mouth in order to breathe.
All of these diseases have the usual symptoms; head shaking, wheezing, sneezing. It's also possible for birds to have two diseases at the same time. A good example is Coryza and MG.
Here's a link for you regarding the respiratory diseases I mentioned above, take a look at them if you wish. As always with poultry respiratory diseases, birds remain carriers for life and stress can bring out symptoms. You will have to maintain a closed flock or cull. Then repopulate in about a month if in fact it's MG.
https://edis.ifas.ufl.edu/publication/ps044