My usually active dog is lathargic. It started about a week ago. First she acted like her hind legs hurt. She stopped jumping and could not jump up on her chair/ bed. We took her to the vet and he said it looked like she sprained her back leg while running. A few days later she started to jump up to her bed again. But now (4 days later) she has started to act worse. She again can no longer jump up. She now is very lathargic and has bumps covering her entire back. The bumps are small and look like pimples or mosquito bites. She us no longer eating her regular food. I am only able to get her to eat a small amount of canned food. I am worried and don't know what is going on.

I would take your dog into the vet. And if you are not satisfied with your vet now, find another one.

Anytime a dog has a back injury, they shouldn't be allowed to jump until the doctor releases them. She may have reinjured herself and made it worse.

She really needs a vet