@BullDog Mom , welcome to the forum. So sorry to hear about your dog, you must be very upset and worried. The vets will never admit that it could be the injection, they would probably lose their jobs if they did. My dog started having seasonal itching for several years now, but I don't want him on drugs and would definitely not give him those shots. I have no experience with MRSA, that is horrible.
I have him on Dinovite daily, use Zymox shampoo and conditioner when I give him a bath, not too often, only when he needs one. What kind of food are you feeding? I also started to switch out his sources of protein, they say that may cause itching in dogs.
I feed Fromm Adult dry food (NOT grain-free), and Wellness canned 95% Beef Dinner, or 95% Lamb Dinner, both of those are grain free. Each year he does better and better with the scratching, initially he was scratching himself raw and I was having to put a shirt on him even though it was summer, but now things are much better.
Good luck with your boy, he looks very sweet.