I had the same thing in two of my chickens. They seemed fine except for the couging/sneezing and some gurgled breathing barely less energy. I am lucky enough to live where there are two avian vets, and I called one for some advice.
Which was to put saline up their nostrils - which I did when they roosted by placing a hand towel around their wings and dropping the saline on top of their nostrils. This did help with the breathing, but it was not the answer.
This went on for about 2 weeks, no change...Not better and not worse. So, after searching the message boards for a while and doing my best to control dust...I brought them into the vet. Even she was unable to be 100% conclusive of their condition. Fecal test came back good.
I was perscribed .15cc ivermectin for gape - it is common here this time of year, as a just in case, but her main hunch was a mycoplasma that had not come into full fruition yet. For this she perscribed 100 mg powder Doxycycline per chicken. The perscribed amount was determined by the weight of each bird and over a period of 8 days.
The appointment was expensive, but the antibiotics were not. They are fine now!!!! More energy and no more coughing and sneezing. And I cought it soon enough that only two of my 4 chicks got it.
Hope this helps.
Cynthia