I am so sorry you are going through this and I can relate as i have two yorkies. One with severe allergies and the other who had a severe case of pancreatitis which led to inflammatory bowel disease. I now deal with specialists such as a dermatologist and and internal medicine doctor and what a difference. I have been frustrated with vets and if i am not happy i move on to another one and take my records. I really hope you can get someone who can help your baby.
Dee Dee had a brownish stuff around her privates and it was immediately diagnosed as a yeast infection and she was put on antibiotics - clavamox i believe.
Also, Dee Dee does the reverse sneeze when excited or agitated from itching so you are right the stress will cause her to feel more agitated and affect the breathing.
Have you tried using hypoallergenic baby wipes fragrance free as i use those on dd's paws daily for her allergies. Also neosporine is a great antibacterial that the vets and dermatologist recommend for when dd itches herself raw from allergies - i put it on her and it is instant relief.
I feel so bad for you as i can completely relate after having the worst year with my boy yorkie dexter and 2 years of allergies with my girl yorkie. You just want to pull your hair out and try to keep from crying.
Hang in there
Oh also the ace is a sedative to calm them down. I hate giving meds as well and always look them up on petmeds.com when i get home from vet. But if she is so worked up from being agitated it is not horrible to use to calm them as the more agitated they get the worse it will get for breathing. I had to give one time when dd had a severe allergic reaction and she would not stop itching no matter what we did we bathed in oatmeal, she had a dexemothesone shot, and we gave her ace for one day til she calmed down as the vet said when they get stressed it agitates them more and they become more itchy and upset. Also, I get freaked out when they get sick and I have learned the more upset i get the more upset it makes them so i have tried to remain more calm and it has helped.
The breathing i have heard steam in a bathroom, putting their face in front of a fan, having a dehumidifier in the room they are in to help sinuses, holding them vertical, and massaging the trachea to relax the trachea. DD gets episodes when she takes temaril p for allergies and gains weight. When she is thinner no issues with trachea. I also talk calmly saying it is ok. All things have helped as every night when we come home she gets so excited she gets a little trach issue.
Hope this helps as you are not alone - i have cried many of nights with my two and felt hopeless.
For Example - easter I had dee dee go into canine hives attack at 2 am and dexter start vomitting at 9 am - it was horrible and a holiday
Take Care and keep us posted