Thank you for the additional information.
I would note that there is much overlap when considering the cause of pain felt in the upper abdomen and lower chest. Conditions in the abdomen can cause chest pain and conditions in the chest can cause abdominal pain. However, you have had a very thorough evaluation for chest conditions, so while I am going to talk about further evaluation of the abdomen, this is because you have already had a more extensive evaluation for chest conditions that can cause pain.
Reflux, or more properly, gastroesophageal reflux disease (GERD), is a common cause of abdominal or chest pain, which can radiate to the side or back. The esomeprazole is a great medicine for GERD, but there is no medicine that works 100% of the time in controlling GERD. If someone has persistent symptoms despite taking esomeprazole, then either it has helped the reflux or this may be one of the small minority of people in which the medicine will not work. If the former, then we should be looking for other causes of the pain, which I will discuss further below. But if the latter, we would need to consider more aggressive care for the reflux, such as augmenting the esomeprazole with a medicine that works by a different mechanism or consideration of surgery for the GERD. A repeat gastroscopy would be the usual method for identifying the persons with persistent reflux despite esomeprazole.
As for evaluation to look for other possible causes, the usual next test that I would consider would be a CT scan of the abdomen. An MRI of the abdomen can be better for certain organs, such as the liver or spleen. But for overall assessment of the abdomen looking for conditions that can cause pain, a CT scan would usually be the preferred test. If there are findings on exam or other tests that raise concern about the liver or spleen, then a corresponding MRI would be appropriate, but you do not mention any such findings thus far.
If you have not had a colonoscopy, this also can be considered. From your description of symptoms, a colon problem would be less likely. But the colon does wrap around the abdomen and if there is no other cause of pain that can be found, it would be appropriate to consider a colonoscopy.
If I can provide any additional information, please let me know.