Reactivity in a puppy

Our german shepherd is 6 months old. We've had him from he was 11 weeks. In the house he's awesome, still has that crazy puppy energy but hes been improving everyday. Fully crate trained, fully house trained, knows commands focus, sit, lie down, stay, wait, get your ball/toy, go to bed, paw and solid recall in the house, in the garden its about 50/50. When were out of the house he's like a coiled spring, reactive to other dogs and even his own reflection, it doesn't appear to be agression (no growling/snarling/no teeth baring/shoulder hackles occasionally raise but not along rest of back or rump) and when were in a dog heavy area he does start to loose interest after 15/20 mins, if its not a dog heavy area he will go off at every one. We are waiting to hear back from a trainer/veterinary behaviour specialist that our vet referred us to, but that could be awhile. Most trainers local to us that have open slots use shock collars or prong collars which we are personally against as is our vet thankfully, so we dont have a lot of other resources available to us. Anyone have any advice in how to help in the mean time.