Can anybody explain what's up with my Stomach?

I've been suffering from this burning sensation in my Stomach (specifically from right beneath my Rib-Cage all the way down to my Abdomen, the center being the place where most pain is located) for two days already, and I don't know what to do. It's not unbearable but it does cause great discomfort..It's painful for me to perform any action that somehow involves the usage of my Stomach Muscles and even after drinking two Advil Pills (two yesterday and one today) the pain doesn't go away. Help?