The data you reported (dull pain/pressure in the chest, no triggers detected, but worsens with exertion or movements) is not specific enough for any definitive diagnosis to be given. However, certain assumptions can be made.


The dull pain in the chest might be due to a pathological process in the esophagus. A tissue putting pressure on the surrounding organs might stretch them enough to cause dull pain.
Various disorders in the heart might also be presented with pain, although the pain is usually described as stabbing rather than dull.


You might want to visit an internist for a physical examination and visualizing methods (barium X-ray, CT scan) to check for tissue inadequately positioned in the esophagus or ,eventually, a mild form of gastroesophageal reflux disease. However, in Gastroesophageal reflux disease the pain is usually described as burning and is associated with meals. An ECG and echocardiography might be needed to check the heart condition.


If nothing is found, then you might be experiencing a condition similar to globus hystericum. Globus hystericus is a subjective feeling of a lump in the throat, when there is none at all. This feeling is caused by various psychological conditions and might need help from a psychotherapist to deal with it. A similar feeling can be identified in the chest, right below the sternum (chest bone). Please note that the psychological origin of the pain can be given only after all other possible physiological causes are ruled out.