Reflux is a common condition, if the pain is coming more from the middle, right behind the
sternum. But a word of caution-- pain and/or pressure in the
chest cannot be ruled out for cardiac causes based on exactly where it is felt; the heart causes 'referred pain' to the jaw, shoulder, and arm, and can mimic pain in the gallbladder as well. Although the positional nature of your pain argues against a cardiac cause.