Of course, I am not a doc, so you will need to have this looked at. However, I do suffer from alot of tummy ailments
so maybe this will help.
One night a few years ago at work, I couldn't hardly stand up from the pain in my upper left side, right below the breast bone. It started in the front and wrapped its way around to the back. After much ado (about nothing it turns out) in the ER a few hours and an Xray later, they determined I had a large pocket gas trapped in the upper quandrant of my large intestine. Apparently, there is some syndrome where this does occur, although for the life of me, I cannot remember what it is called. I did see my Xray, and it looked like I had swallowed a small balloon.
Since yours is in the back however, you shouldn't rule out a possible kidney infection, depending on where it hurts. Definitely get checked out.
Eh, what the heck