OP, I agree with dogma. You have to give your dog something to do before he focuses on another dog. It sounds like you are maybe pushing him past his threshold, as well. He probably cannot handle seeing a steady stream of dogs so close to him. Try taking it back a few steps. Go to a park where there might be a few dogs (NOT a dog park), and work on your engagement with him. Keep him at a pretty good distance from other dogs. You probably need to up his obedience overall. He’s young, things are not proofed yet. Time to start proofing what he already knows so he is reliable in all situations. If you have not already found a good trainer, it might be wise to do so. He’s entering into the most buttheaded part of adolescence, which can be rough.
Train the dog in front of you.