On the off chance that someone may have had this problem.........three weeks ago I was playing cards until 3AM and I noticed that my kidney's were getting more tender as the night and morning progressed. Being a jarhead, I dismissed it as entirely to much laughter. It caused me to leave work early on three different occasions and take days off and lay in bed for two others. So far, I've had a cat-scan but nothing was found. I've dismissed stones and the big C (as I've had a battle and fortunately won in the past). To have the doc tell me they found nothing in the scan as they are still tender is frustrating. I am better but, still concerned. My blood work hasn't come back yet so, I'm just waiting with frustration.