Possible sick baby zebra

[nelloyello11]

I have a baby zebra (almost 6 weeks old), who may be sick. On sunday, we separated the three babies from mom and dad, as mom was getting aggressive toward the little ones and they all neede more space. They have been eating and drinking on their own since then and are all very active.
However, this morning, I noticed that one of the babies seems to be breathing heavily, and is puffed up. She is eating and drinking and pretty active, though maybe not quite as active as the other two; it is hard to say.
Any suggestions as to what this might be?
I also noticed that she may have lost a couple tail feathers, though I don't know if this is related....
Any help will be appreciated.

[nelloyello11]

Also, sometimes it looks like she is trying to cough something up; she is not making any coughing noises while she does it, but it looks like she is coughing or gagging something up....
Please help!

[L in Ontario]

I would think she may be moving food from her crop to her stomach - that can look like gagging.

Put a heatlamp on the cage at one end of a perch so they can go to it if they need some extra warmth.

[nelloyello11]

Okay, I just went out to see what I could find as far as medicine in case she is sick. I was able to get some Ornacyn plus powder.
When I got home, she looks worse. Her mouth is open when inhaling and I can hear a clicking noise.
I know this is a tell-tale symptom of air sac mites. Is there anything else it could be?
What is the best treatment for baby birds with ASM?