Vets aren't sure what's wrong with my dog

Hello everyone, I'm at a loss on what to do anymore. My dog Ace is 4 years old and is a a German shepherd husky mix. His symptoms are lameness, struggles to go up and down stairs, and if I try lifting his tail he'll cry as well as when I try stretching his back legs as he can't really sit only lay down or stand. He hasn't ran since mid July as he can't seem to do it due to pain in hind legs.

I have taken Ace to the vet multiple times throughout this unfortunate journey and his blood tests, urine tests, and stool tests are all perfectly fine. His lymes disease test was also negative. He had an ear infection early on and it's been taken care of but his pain still lingers with his hind legs.

He was given different antibiotics and pain meds to help any issue it may be and nothing has worked. They also gave him nerve medicine and nothing. He was perfectly fine before these issues started, the first day of an issue is he was limping his front left paw and then that stopped and it was his back left paw. He stopped limpijg early on in July and the areas that are in pain the most are his hind legs as he will cry or moan if I touch the area or if I try massaging or stretching his legs and muscles.

He eats and drinks water fine but he has lost almost 10lbs since these issues started. He gets excited to go for walks altho I have made them shorter to not over do his walking. W

As I've said, he can't run, if he jogs it looks like he's hopping on the back legs or speed walking. He can bark but not as loudly, not sure if that's causing discomfort when he does it. He poops and pees fine and there's nothing unusual about his poop or pee.

He has lost strength in his hind legs and has lost weight. I am thinking of asking a vet for some muscle relaxing medication to see if that would help. If anyone here can possibly help out or tell me what should be done next I would greatly appreciate it as the vet bills have added up throughout these past few months and I don't see much progress with Ace.

Update: It seems he has inflammation on his inner thighs either nerves or muscle as if I try moving my hand around the area he yelps and I can feel his pulsing. The vet gave me gabapentin 2 pills 3 times a day and carprofen twice a day. Hoping the higher doses help Ace out.