Well first I would find a new vet, that is just not cool.
I am not a trainer, not an expert and according to some folks on the forum neither bright nor sane, so take my advice for what it's worth
I can only tell you what worked for me. Everyone hates my dog. My husband refused to live with her, we went through half a dozen vets, trainers won't touch her.
She is sweet, well mannered and friendly as heck. At home where she is comfortable. Out in the world she is a disaster. She pulls, she lunges, she pitches fits that rival those of the most unruly toddler, shrieking, screaming, throwing herself on the ground. She snaps at people, she barks and snarls at other dogs.
I have a bit of an advantage over you. She is barely 50lbs, I can pick her up.
I conditioned her to a muzzle, step 1. She wears a basket muzzle in public and an exam muzzle at the vets. It is part of her routine, she understands that and she is fine.
We worked really hard on focus, step 2. Look at me, watch me. She is conditioned to focus on me when crap gets her worked up outside. So if another dog pops into our view she immediately looks at me. We also worked on thresholds. How close is too close? When we started if she could see it it was too close, yesterday morning we had a loose dog 10 feet away challenging her and although she did bark back a few times, she held her sit and stayed mostly focused on me.
I walk her on a prong collar most often, step 3, although lately we have just used her martingale and she is fine. Since no one else would help me I reached out to a member here on the forum. He helped me immensely to learn how to fit and use the prong and was an awesome resource. The prong allowed me to quickly and properly correct poor behavior and actually relaxed her so she could enjoy the world.
One of the issues with fearful dogs is that they work themselves into such a state that learning is impossible, that was where the prong helped me. The other thing I learned was about stress. If we had an incident or a really bad day I learned to skip the walks for a day or two to allow the stress hormones to dissipate and her body get back to level.
If you can work with a good trainer it would help, the problem there is more bad ones then good ones so if someone on here has a recommendation perhaps that will point you in the right direction.