my husband had kidney stones a few years ago. His started out w/just a dulling pain in his side. It didn't take long for the pain to worsen. We ended up in the er. Maybe this will help.
If it was liver pain, it would probably be worse, if you press strongly with tips of fingers of both hands on area under the left rib cage. The next thought is gallbladder - pain would be much more localized, on the middle of the left part there, and much stronger on pressure. This gallbladder pain would be worse after fatty meals.