I also have had upper left side pain, specifically under my ribcage, for at least the last 3 years now. It comes and goes, but is present much more frequently than not. I went through a whole battery of tests when the symptoms first appeared (i have crohn's disease, but the pain is not typical for my case). None of the tests showed anything (cat scan, colonoscopy, endoscopy), and my blood tests were normal. My gi doc told me it was probably "splenic flexure syndrome", which is basically gas getting trapped in the portion of the colon that loops around under your spleen. For lack of another cause, and due to the longetivity of the condition, I assume that it is nothing more serious, but sometimes I have my doubts. Anti-gas meds don't help -- the only total relief I get is when I am out doing something active - playing tennis, jogging, etc.