Hello. Thanks for the question. I'm sorry about the wait. Later at night there are fewer vets online so it can take a bit longer than we'd like.
I'm a little more concerned with his back. It could be the hip, but back pain is more likely to cause reluctance to jump up and overall just not wanting to move. Like in people, back pain can be pretty crippling and it just hurts to move. Often times these dogs come in with reluctance to jump up, reluctance to do stairs, an arched back and trembling.
The diagnosis is made on neuro exam. We feel for back pain when pressing straight down over each individual spinal segment. We also check neurologic reflexes to make sure the spinal cord signals are processing normally.
Most dogs do well with exercise restriction for 1-2 weeks along with pain management. I typically use a combination of an anti-inflammatory (Rimadyl) + something for nerve pain (Gabapentin).
I would just keep him quiet until you can see your vet. If it does end up feeling like hip pain, x-rays would help. Otherwise, the pain meds and rest should get him back to normal.
I hope this helps, let me know if you have any other questions.