Center of your lower back? Can't crack your spine, and massaging the muscles does nothing?
Like everyone else said, kidney infection. And you want to take this very seriously! Drink LOTS of water, avoid energy drinks and sugary beverages and all that junk. Cause if you don't, the infection WILL GET WORSE. It can get so bad you can't even walk without being double over in pain!
Also, damage to your kidneys is CUMULATIVE. Get lazy about staying hydrated again? It'll come back with a vengeance!
This is nothing more than a thought terminating cliche. As such, it's completely worthless.
Edit: lol...funny how y'all talking about...nothing at all ¯\_(ツ)_/¯