Need help with chicken cough

[Mithryl]

So I have 6 hens, 2 months old. One had developed a short cough/hack occasionally which I think I caused from dust because I read somewhere to mix DE in with the bedding. Now I have noticed another chicken does it. There are zero other symptoms from any of them other than the two that will occasionally cough/hack. I have been reading and it ranges from 'they may just have some dust, they're fine' to 'it's respiratory disease cull the entire flock'. How do I know what I'm dealing with so I know how to treat it? What causes it? Aside from the dust issue (which I haven't done since) I keep their coop clean, completely changing bedding every other week. Who would I contact to find out and how much would it cost? There aren't any farm vets in the area.

 

[Eggcessive]

It can be common for any chicken to occasionally sneeze during feeding times or from dust. If one does it every few minutes there may be a respiratory virus infection called infectious bronchitis. More serious diseases such as mycoplasma (MG,) coryza, or ILT can cause more severe symptoms such as gasping, wheezing, nasal drainage, eye bubbles or foam, gunky eyes with swelling, and others. It would be good for you to read through some of the common diseases, and know what symptoms to look for to tell if it is serious or normal. DE is pretty useless, other than being a danger to breathing, so I won't buy it. Here is a good reference with the common diseases and symptoms:
http://edis.ifas.ufl.edu/ps044