the problem could be a number of different situations. it could be muscular, pinched nerve, a disc pressing, etc. go see a chiropractor for a couple of visits and see if that offers you some relief. they would help you & determine what could be the cause. in the mean time, try lying on the floor, (carpeted), on your back to help straighten out your spine and see if you get any relief doing that a couple of times a day for 15 minutes each session. it may help some. other back exercises might help you too. it's best to have your doctor check it out, though (better safe than sorry!)
It could be that your sleeping wrong, or that your spine might be a little bended, just go to the docto and figure it out, he/she wilp give you a better answer and get you treated.
We really don't know...you'll have to have a doctor look at it.
This reminds me of an embarrassing story I have. :D
I dont know, its probably sore?