I'm by no means a training expert. I just want to give you support. You are not alone by any means. Many on this forum have leash reactive dogs. Hopefully, they will come and share with you their experiences and training techniques.
Personally, when my GSD was just a 6 month old pup, I thought she was becoming leash/dog aggressive. Fortunately, I found a great trainer and he told me she was not leash/dog aggressive at all. She was just excited and hadn't learned proper manners.
Step back, find a good trainer in your area (if you let us know your general area you will likely get trainer recommendations). With proper training, it is likely things will get much better for you and your dog.
Thank you for rescuing!