Hope you get things sorted and have your boy looked at by a vet without him freaking out. I would also look at changing vets or a mobile vet if you can find one.
We rescued a dog many years ago that had been so badly abused that anyone or anything would make him cower and wet himself. We found a mobile vet who came to our house for consultations, I spent some time talking to her prior to her visit and explained his fears. From her first visit she was such a lovely gentle lady and he let her examine him, take blood samples, even take him away for surgery once when he ate most of a tennis ball and its passage through him caused lots of problems and pain before it's surgical removal! He used to get so excited to see her, she'd always bring a treat and make a real fuss of him.