If you get an upset stomach several times a week and experience other symptoms such as constipation, diarrhea or severe stomach pain after eating certain foods, you may have irritable bowel syndrome (IBS). Other telltale signs of IBS include:
Bowel movements that feel incomplete
Changes in stool consistency
Passage of mucous fluid
Stomach fullness or bloating
According to the National Institute of Diabetes and Digestive and Kidney Diseases, a diagnosis of IBS requires that you experience symptoms for at least six months and at least three times a month for the last three months.