prelim hip/elbow x-rays. They can be done when he's 6 months but be sure to use a qualified vet, not all will position right.
I agree on the cow-hocks....that is usually something that doesn't go away, it's in the dogs structure. But you can strengthen the rear end, which looks like your pup lacks muscle as well. Bunnyhopping may go away.
Good to read you're feeling better! Nothing like being sick with a young energetic pup in your life.