Well saw the company Dr on my way out of work today.  (We're self insured, so we have employee health on site).  Dr said I yanked a tendon real good.  Gave me a bottle of Flexirol, said to take 1/2 a pill.  Wow, I slept like a rock today and my back is much improved.
As Maverick said, he said the same...kudos for going to the gym, but SLOWLY phase in the increases!