How Can I Tell If My Yorkie Has A Cold?

Are you certain your dog is attempting to cough and not gagging?  Sometimes it can be hard to tell the difference with these guys.  A hacking cough, lethargy, and anorexia are commonly associated with kennel cough.  Dogs usually have a deep cough that sounds like a goose honking.  This cough can often be elicited from palpating their trachea (throat).  Nasal discharge is often present.  This is a contagious disease between dogs.
Gagging, vomiting, or difficulty swallowing are not seen typically with kennel cough.  If a dog has something stuck in the back of the throat they are bothered constantly.  They will smack their lips, drool, and gag much more frequently or constantly than dogs with kennel cough.  This does note sound like allergies.  Environmental or food allergies in pets does not cause lethargy and anorexia.
If your dog is not eating or drinking for any reason she needs to be seen by a veterinarian for diagnostic testing, appropriate treatement, and supportive care.

You can't give your dog benadryl

It could be a cold, but it sounds more like kennel cough to me, I would have her checked out if I were you, as it can be fatal. Hope this helps.