What Causes Dull Ache Between Nipple And Sternum?

I have been having a dull ache between my left nipple and sternum for about 4 or 5 months. It seems a little sensitive to the touch and I can feel a little ache when I swallow food in that area. Sometimes I dont notice it and sometimes, without eating, it aches a little. I think I have some acid reflux because I could taste something bitter up in my throat and I have been taking prilosec otc for a week and it seems better. In 2009 I was diagnosed with silent reflux so Im wondering what the dull ache might be.