I too had pain nearly constantly in my upper left abdomen. Finally I got my doc to do an Upper GI endoscopic peek, as well as a full abdomenal sonogram. They finally found the problem, or should I say problems. I have an enlarged liver, enlarged spleen, hiatal hernia and nodular Brunner's gland (which means polyp-like growths) and which is thankfully benign.
Talk to your doc, insist that he do at least the sono on you (though I'd shoot for both).
"Bleh" sums it up nicely, don't you think?