Thanks for the additional information. It is helpful.
I'm glad to hear that the puppy seems to be doing a bit better. I do think the dosage of aspirin given seems a little high. Buffered aspirin can be given to a dog with a dosage of up to 5 mg per pound every 12 hours. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet. The aspirin may need to clear your dog’s system before other medications can be given, so keep that in mind if you decide to give aspirin and be sure and tell your vet when your dog is seen. Read side effects and precautions here.
Normally we wouldn't even give this to a puppy this young. Let me tell you what might be going on. Sometimes when a dog has pups, they will nip to hard or bite when the pup is first born or puncture the skin carrying the pup. when a puncture occurs, bacteria gets into the wound. The outer wound heals but the bacteria under the skin continues to multiply forming an abscess. This abscess can interfere with the way the bones
are forming and lead to pain for the puppies.
Now often you will find swelling but not until the pup stops being able to move a limb. Another possibility is the pup climbed on something and fell injuring himself. For a pup, a bruise or cracked bone can stop them from moving around normally. I would not give any more aspirin at this point. Monitor him and see if he continues to do well. If he continues to move around and doesn't become lethargic again, perhaps it was a bruise since you don't feel any swelling. However, if he deteriorates again and seems to have problems moving, you will need to have him seen by your vet. If an abscess is present, your vet can give amoxicillin
to help the pup battle any infection present and get him back to health quickly.
I wouldn't wait too long as an infection close to the joint might cause permanent damage to the way the bones fit together.
I hope this information is helpful to you. If you need more information or clarification, please reply and I'll get back to you as soon as possible. If you are satisfied, please take the opportunity to rate.