Respiratory illnesses can affect production. If it's something reoccurring, then you may be dealing with Mycoplasma. Amoxicillin usually is not effective against Mycoplasma since it has no cell wall, but since you started the meds, I'd see if it makes a difference.
If not, then you can try Tylosin or Tiamulin (Denagard) to see if that helps.
If not, then you can try Tylosin or Tiamulin (Denagard) to see if that helps.