Young dogs around this age can be a handful. Some call it the teenage phase. Others think it is total fear-aggressiveness, some say dog-reactivity. I really don't know. My suggestion would be to take your dog to classes and continue to take him to classes, where he is working in a class with owners and dogs -- try not to overwhelm, do not let people come right up at this point with their dogs, just get him used to seeing other people working with their dogs.
If you keep going, the dog learns a lot, gains confidence, and you gain confidence, and one day you wake up and say, "Wow, my dog is awesome!" I think it is one part natural maturation, one part continuous good exposure to common events without overwhelming the dog, one part improved leadership, one part improved handling, and one part training in the dog. The good news is that the training classes themselves can get you to the exposure, the improved leadership, the improved handling and the training in the dog.
Good luck with your dog.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC