The diagnostic method that doctors use are always the same but when it fails, doctors find themselves in a very difficult situation, because in general terms they can't authorise investigation unless diagnostic test provide some evidence. When one starts to diagnose oneself without experience of others it is fraught with dangers. Nevertheless this is what we have to do.
You need a very detailed description of the pain; exactly where it is, when its worse etc. For example does the pain rise into the rib cage or stay on the rib margin. Are there any tender points along the ligament lines, does the pain travel to the shoulder top, under arm or between the shoulder blades. Is it eased by laying down on ones back or leaning forward.
This is the pain map for our internal organs
The gallbladder is always a firm favourite but is always supported by ultrasound or blood-works evidence. I've had gallbladder pain and it is nothing like the gnawing chronic upper abdominal pain. Also bear in mind that if you have good stools then the gallbladder is less likely.
Stomach and duodenal ulcers can be more easily diagnosed and treated because they are caused by a bacteria. You can research "Helicobacter pylori" in detail but remember the Internet is full of horror stories not the mundane. Eating broccoli, sprouts, and cabbage regularly can halve the effects.
Muscle strains can be a very difficult problem to find and can be caused just as easily by poor posture and worry as straining. They can even be triggered by sneezing. They can be present for years until they are treated with muscle trigger point massage. The pain caused by upper abdominal muscle knots or "trigger points" can mimic heartburn, hernias, gallstones, and heart problems. They can be made worse by exercise until the problem is found and massaged away.
Other problems include a hiatal hernia which can mimic digestive and organ problems. There are other rare hernias that are always dismissed by doctors because they are rare include anomalies with the ligaments that hold the liver in place that are interconnected to the abdominal wall and sternum area. There is very little to read about these conditions and diagnoses is almost impossibly because of the lack of information and expertise. Only when it gets so bad that one is double up on the floor does the doctor act.
Poor blood flow to the internal organs or restricted nerve impulses can upset digestive system and refer pain. Some people with spinal injuries sometimes get unexplained abdominal and organ pain.
Keep the faith.