I also like puppies very much. Dogs have been kept at home since childhood. According to what you said, it may be a cold or enteritis. It is normal to limp after infusion, and the leg will return to normal in a few days. Now the doctor may not have found out the cause, so the infusion is useless and the course of treatment is delayed, so the dog's condition is aggravated. I suggest you go to a bigger and more regular hospital to see the dog as soon as possible. After all, dogs can't resist for as long as people, and dogs may not be able to resist for a few days when they are sick. I hope your dog will recover soon.