From a wrong diet to a flu to a pre-existing gastrointestinal condition, many factors can cause your belly to hurt. A stomach pain is usually benign and easily treatable with changes in diet and medications. But what if your stomach pain is persistent, feels unusual, and disrupts your daily activities? What if the related symptoms indicate GERD (gastroesophageal reflux disease) or something more serious like stomach cancer? How do you differentiate between the eerily similar symptoms shared by both the conditions?