First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes.
The back pain that you describe may be musclo-skeletal or related to a disc/spine problem. The feature of pain worsening with exertion of the area is very common with both. I would suggest an MRI of your Thoracic and lumbar spine to evaluate. I does not sound like you have a severely pinched nerve, or you would expect radiation, weakness, and/or numbness.
The episode that you describe, waking up and one leg does not work, is concerning. It could be something as benign as you slept on it funny (if you sleep on it wrong, you deprive the blood supply and it will feel weak and numb when you wake up, then return to normal as you shake it etc.). It could also be a warning stroke or a "TIA" (transient ischemic attack). Being that you are 28 (quite young) stroke is less likely, but still possible. I would recommend that you see a neurologist and discuss your need for a MRI of the Brain to look signs of minor stroke damage, (after your exam of course).
I hope this has been helpful.
I've experienced similar type pain. Mine feels like someone is jamming a broom handle deep in to the right side of my spine in the thoracic area. I too was told it was muscular. I had a whiplash injury 11/05 and that is when it started. I too had a thoracic MRI which was normal. Another MRI was ordered but for the C-spine which showed three protruding discs, two of them having a mass effect on the cord. I had been through PT & chiro care prior to my ACDF C5-7 surgery back on 6/22/06. Nothing helped that intermittant stabbing pain before surgery. Now, maybe it's just coincidence, but that stabbing feeling no longer taunts me even though I'm still dealing with most of my other c-spine pains.