I too have been having pains in the sternum area for a long time,. its very scary i know man. its hard to pinpoint exactly what is causing the pain. acid reflux? gas? anxiety? theres many things that can cause the problem.
You may even have LOW stomach acid. I would try a pill of beatine HCL with food, if it causes you a warm sensation in stomach that means you do not have low stomach acid, but if it doesnt, then you have low stomach acid. low stomach acid and acid reflux have basically the same symptoms and are often misdiagnosed with each other.
if the pain is between the breasts when you push down it may be costochondritis. which are inflammed muscles. not sure if that helps.