I Have Been Experiencing Mid Back Pain Radiating To The

I have been experiencing mid back pain radiating to the ribcage on the left side of my body. The duration has been on and off for nearly one year. I had a chest X-ray approximately 9 months ago, clear of any major concerns. The past few days, the discomfort has increased. Various laying positions and sitting for too long will cause the discomfort to worsen. I take OTC anti-inflammatory meds to help with the discomfort. Also, if I lay on my stomach and move in a certain position, it feels like there is something 'popping' in the left side in my mid left back/rib area. What could this be and what are my next steps?