If your having trouble eating and hurting on your upper left side of your stomach and the doc does a upergi and finds nothing what could this be?

Lots of reasons...: Have you undergone upper endoscopy to rule out gastric disease missed on x-ray or colonoscopy to assess the splenic flexure of the large bowel? Do you have underlying irritable bowel syndrome? Is your distress worsened or improved by meals, activity, deep breathing, palpation of ribs? Have you suffered any physical trauma recently to the area? What medications have been tried, & which have helped?

Multiple possibiliti: Not sure what exactly you mean by "trouble eating" but a more detailed exam is an egd (scope that is passed into the stomach while you are asleep) an this may find the cause. Also occasionally colon issues can cause pain in the left upper quadrant as well and a colonoscopy may be suggested. A spleen issue may be the culprit and an abdomen ultrasound may be helpful in finding out what's going on.