What Causes Pain Behind Breast Bone Radiating To Right Side Of Rib Cage?

I had a colonoscopy and 11 days after that I started having this pain behind my breast bone in the center of my chest even when I swallow my own saliva. I had an endoscope to see the problem was.Only found mild gastrits. No reflux. It has been 4 months now and I still experience pain, it also radiates under my right side rib cage. I had gallbladder removed 2 years ago. Been feeling bad ever since. That is why I had colonscopy. Please help. What could this be?