Hello According to your history of illness mentioned in the query , this nagging dull pain in the stomach with pain in the back may be due to these possibilities , these include: 1 The first possibility is of peptic ulcer disease ( hyper acidity ) or Hiatus hernia . Diagnosis can be confirmed by upper G I endoscopy. Try raising the head of your bed about 4 inches with blocks. It also might help to avoid eating or drinking for 2 -3 hours before you lie down. To control stomach acid one should not drink alcohol or drinks with caffeine in them or eat chocolates or spicy or greasy foods . Also take some antacid but if symptoms are severe you may need drugs like proton pump inhibitors like pantaloc-d , once or twice in day depending on the condition of symptoms and intensity of pain. 2 Overeating or tension or anxiety are other such reasons which produces such symptoms. 3 The last possibility may be of pancreatitis as it may cause upper abdominal pain ( on left side ) which is worse when bending over or sitting . Diagnosis can be confirmed by measurement of lipase and serum amylase enzyme. Deal as mentioned above. Hope this will help you.