I can't really help as far as vets go. But I did write recently that doctors don't seem to care for the person (or animal) as a whole.

Their job is to keep the physical body going. Then on to the next physical body, be it an animal or a person.
We have become separate "parts" to the medical community....

This has been my experience anyway.

What you need is to find someone who's actually sympathetic to both you and your cat. Is there a reason you have to see a dermatologist specifically? Why would the testing have to be redone?

We are people and should be treated as people...especially when it comes to us being caretakers because a caretaker is a patient of sorts, too. We need support of all kinds.

It's not insolvable. Are you able to go to a clinic just for them to administer the shots? Or your local place? Someone other than your current vet.

Once again, just suggestions and sympathy.....

Hugs to you.