It could be just the sort of muscle stiffness we get when we over do it. After vacation last year, it took at least a week before I could move without hurting.
I would try to keep him quiet and if not better by Monday, call the vet.
My guess is he would be better off without any pain killer, especially Ibruprofen or acetoaminophen. If you absolutely have to give him something, try aspirin, 1 mg per 5 pounds of body weight. Maybe a baby aspirin an 83 mg tablet would be right for a 21 pound dog. Better, nothing at all without talking to the vet.
I would try to keep him quiet and if not better by Monday, call the vet.
My guess is he would be better off without any pain killer, especially Ibruprofen or acetoaminophen. If you absolutely have to give him something, try aspirin, 1 mg per 5 pounds of body weight. Maybe a baby aspirin an 83 mg tablet would be right for a 21 pound dog. Better, nothing at all without talking to the vet.