Advice for needed

Hi - i have a puppy 15 weeks he was born in our care, he had trouble walking to begin with dragging his hind legs struggling to stand ,he eventually did walk but seems weak on the back legs , he has been urine incontinent always and recently becoming less able
To control bowels also , we have had him at a local vet whom suspected his kidneys were very swollen other than that the vet hasn’t given us much advice, also the puppy can be quiet aggressive to touch towards all , he eats very well but can appear thin , any advice is greatly appreciated