possible IB outbreak

[PeAckAnBiTs]

So I got a small flock of about 10 six month old hens an pullets...5 WLH 3 Polish 1 silkie 1RIR. 1 pullet got sick 7 days ago so I seperated her an started giving her antibiotics an vitamins did not cull. Everyday sense then a bird a day has gotten sick an I seperated her from the main coop. So I have all 7 sick birds in a seperated coop. I'm leaning towards possible IB just from research as I don't have money for any kind of test.
SYMPTOMS- snotty nose, weezing/ rattling breathing ( worse at night), not eating, shows no interest in treats really. That's it.
MEDICATION- Tylan 50 more as a secondary treatment cause it doesn't seem to effect the illness. And I been giving a viatim boost in there water .
I also have to force feed them every night bc they have empty crops when they go to roost. Dose anyone no how long it takes IB run its course..open to any an all suggestions. An on a second note the first pullet to get sick seems to be getting better..

 

[Eggcessive]

It's hard to tell infectious bronchitis from other respiratory infections such as MG, ILT, and coryza depending on how mild or bad the particular strain is. I would recommend getting a sick bird tested to make sure of what you are treating. IB lasts 3-4 weeks, but it can be complicated by other secondary infections, such as MG, coryza, E.coli, etc. Your state vet or veterinary college could recommend how to get them tested. Here is a link for that:
http://www.usaha.org/Portals/6/StateAnimalHealthOfficials.pdf

 

[PeAckAnBiTs]

I been reading how you give tylan 3 to 5 days. Would it be a problem or issue if I went more days