I’m still thinking virus. Back not so much. Any type of flu will find out your weak point and cause pain. But it could be food poisoning or even a kidney stone. They hurt like hell to pass. The odd thing is it will go away and you still won’t have a clue. You have to give it time and the body will use its full immune defense against the problem. You could go on antibiotics as a precaution. Not really a good idea though. Take two aspirin and we ‘ll see you in a week is the response I usually get.