Welcome to Justanswer! I am Dr. Altman and happy to assist you both today!
I am so very sorry to hear about your little one. It sounds like he has had a very eventful month! My primary concern is an injury to the back back, not necessarily doing something like jumping off the furniture and crying out, they can be walking around the house and have a disc herniation because of their anatomy. It is possible it is a neck issue related to the original injury and the pain medication was masking his initial discomfort.
Here is more information on this condition:
Ideal is to return to your veterinarian and have him evaluated for this new development. Then your vet can diagnose the issue and reinstitute pain medication or any other medications deemed appropriate. Until you are able to do this please restrict activity (which often they are already doing themselves but that means no steps/ stairs and only carrying to go potty) and rotating warm and cool compresses on the neck and back in ten minute intervals to reduce pain and increase blood flow.
You can also do light circular massage up and down the neck and back to stimulate blood flow if this is not too painful and will allow it.
To pick your dog up please use one hand between front legs and then scooping behind back legs to avoid pressure in the middle of the back. I have actually trained my little dogs to put their front legs on my forearm to minimize pressure on their backs and the associated discomfort. Often what is happening is being picked up under the arms or chest causes compression of the lower neck and back which results in pain. My dogs definitely can cry out as you describe if picked up in this way as well due to chronic pain
Please let me know if you have any additional questions I can assist with. I hope you are able to get your little one comfortable soon, truly.
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