What can cause pain on your left side under your rib cage?

This is not an every day occurrence, but when it happens, this pain will wake me. It is a dully, achy pain that radiates from my left side, underneath my rib cage, around to my back. The pain reminds me of gallstones, but I had my gallbladder removed years ago.
Update: I was wondering, if it could just be caused from gas. However, it is sore to the touch. Would gas cause that?
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