What Causes Pain In The Back Just Under The Ribcage?

Hi, may I answer your health queries right now ? Please type your query here... I have been having pain on the right side of my back just under my ribcage. It is intermittent, but sharp. I can sometimes feel it when I breathe and then it's dull. I can get the sharp pain if I move certain ways, but they are not in ways that are unusual. Could this be due to aspartame? I first thought that it was a muscle pull, but it is going on > 2 months and is not getting better. I drink a lot of sugar free hawaiian punch drink mix that you mix in bottles of water, and one cup of coffee 5 x per week with 3 artificial sugar packets in each cup. Please help.