I understand you are stressed
There are many respiratory diseases that have similar symptoms. Mycoplasma, ILT, Infectious Bronchitis and Infectious Coryza are a few of the more common ones.
Antibiotics
may help with secondary infections associated with respiratory diseases, but will not cure them. Birds being carriers needs to be taken into consideration depending on what your future goals are. If you plan on selling/giving away hatching eggs, chicks, started pullet or showing birds then getting some testing done would be a very good idea.
You can try injectable Tylan50 to see if it helps. You need to separate and treat only the birds that are ill and have symptoms. Weigh each bird to determine they are getting the correct dosage. Injectable Tylan50 dosage is 1cc or ml per 5lbs of weight, given 2X a day for 5days. This can be given orally or by injection 1/4" deep into the breast muscle, alternating each side.
I encourage you to do some research/reading on the various illnesses and compare symptoms. Testing can be performed by your state lab.
http://edis.ifas.ufl.edu/ps044