There are many organs under your right breast, such as gallbladder, right kidney, muscles, part of the lung and liver. The common causes of pain under right breast include hormonal changes, heartburn, trapped gas, and stress. Mar 17, · Sternum or Breast Bone The organs in the thoracic cavity comprise of many critical organs of human body including the heart and lungs. This is the secondReviews: 6. Although referred to as the breast bone, the sternum does not lie under the breast but rather in between the breast, extending above (manubrium) and through the cleavage in women. Causes of Breast Bone Pain. Heartburn or reflux is the most common cause of a burning pain along and under the breast bone as a result of esophagitis. .