My dog has had this happen twice now. She had rads done and it was neck pain. It was horrible to watch and hear her in pain. Anti inflammatories and pain relief (tramadol) were given, and strict rest. It took her a few days but luckily she did get over it. I thought she had hurt her leg to begin with as she wouldn't walk on it and screamed but u could see on the X-rays where she was sore. Hope your little one feels better soon.