This is why people need to never ever take in birds or babysit others birds, because now you’ve most likely infected your entire flock. If you take in ANY new birds, quarantine should be #1 priority with good practice of strict biosecurity.
Chronic Respiratory Disease (CRD), or most commonly known as Mycoplasma Gallisepticum (MG). MG is a bacterial infection of poultry, affecting all different species of birds. This disease is most commonly given from infected parents to the offspring, as the MG bacteria can be transmitted vertically into the eggs of developing embryos, making any chicks that hatch, always infected and sick with the bacteria. So please please PLEASE don’t breed from your sickly infected flock. MG is a chronic disease- meaning, that you can treat or have the symptoms go away, but whenever the bird gets stressed again, the symptoms will keep coming back or get worse. All “recovered” like birds, remain lifetime long carriers of the MG bacteria, spreading and shedding it through their feces, feathers, dander, respiratory secretions and other bodily fluids. This is a lifetime disease of poultry and is incurable. Since MG is a bacteria, antibiotics can help keep symptoms at bay until the symptoms resurface. Keep in mind that over-use and/or misuse of antibiotics also creates antibiotic-resistant bacteria, making the disease harder to treat than before. It’s critical in poultry to get any sick or symptomatic birds tested to find out which specific disease they have as soon as possible.
Here's more information about MG:
https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/poultry/FS-1008 Recognizing and Preventing Mycoplasma gallisepticum (MG) Infecti....pdf
https://www.freedomrangerhatchery.com/blog/protecting-your-flock-what-you-need-to-know-about-mg-ms/
https://afarmgirlinthemaking.com/respiratory-conditions-poultry-mycoplasma-in-chickens/
https://m.facebook.com/groups/381727643241021/permalink/382070023206783/?ref=content_filter
https://m.facebook.com/groups/381727643241021/permalink/405654594181659/?ref=content_filter
Best options you have really is you can keep a closed flock with treatment until all birds pass on their own and don’t breed to sell chicks or giveaway birds. Or you can cull your entire flock. If you’re in the USA, most states have MG listed as a reportable disease, which can lead to another can of worms if someone were to report. I would cull the sickest bird and send it off to your state of Agriculture for a necropsy to be done with testing specifically for MG, MS, ILT and IC.
Just wish it didn’t have to be us to do the dirty work 
