How do I determine if it's allergies or a respiratory infection?

[GoatTraveler]

My 3 year old Welsummer is lethargic lately and last week I noticed she was only breathing through her beak (and it wasn't warm here in NorCal last week). I have been applying VetRX throughout the day for the last 3 days and putting it under her wings in the evening. She seems better but upon close observation, her breathing is labored. She also continually shakes her head as if she has the sniffles. Is this a respiratory infection or seasonal allergies? She is eating, drinking and pooping, but is moving very slowly. And, she sits in the dirt while the others free range. I can tell she isn't really herself. Any advice?

Edit: added photos. I occasionally see some liquid come out of her nose but since using VetRX, that hasn't happened. There is plenty of ventilation. I keep the coop and run very clean (poop gets picked up 2x/day). There is dust from the dirt box they use for their dirt baths and the run is dusty because it's all dirt. They've been in this particular run for almost 2 years. I also occasionally use DE in the run/coop after cleaning. No mold either.

 

[Eggcessive]

Can you see any mucus in her beak or nostrils, swallowing mucus, or bubbles in either eye? How is the dust level, ventilation, and is there any mold? Pictures of her face might help.