FWIW, the reason I said I wold be more suspicious of mycoplasma is based on something I read on BYC and that was someone who talked to a lab and they said that they didn't see too many cases of coryza. Another thing I read was that coryza has an odor, which I don't think you mentioned. I'm not an expert and have zero experience treating my own for respiratory problems, so please do your research and if possible, have some blood sent off to a lab for testing. 
-Kathy

-Kathy