What is the cause of my chronic stomach ache?

Many things. Many people have trouble with gastritis or reflux, due to hyperacidity or making too much acid. It can be due to a medical problem like zollinger-ellison syndrome, but most are due to the food you eat, or when you eat it. Numerous medications will help with it. Talk to your doctor about it.
Go figure... I will definitely need more information to answer that. The sky is the limit on that ranging from irritable bowel syndrome to endometriosis etc. Let me know what your symptoms are, what work up has been done and treatment tried.

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I have chronic back pain, sometimes it causes a stomach ache. Is this a concern?

Back and belly. Back pain associated to other symptoms needs to be investigated there is a correlation of GI conditions such as inflammatory bowel disease that are related to arthritis .a gluten free diet trial may ameliorate both you may need imaging studies such as ultrasound or ct check your lipase to rule out pancreatic problems. Read more...