I Am A Healthy 55 Year Old Woman, Recently Experiencing

I am a healthy 55 year old woman, recently experiencing feeling of heartburn, which settles by drinking water, taking antacids. Now for the last day I've got pain in between my shoulder blades, on my back muscles - does not feel like my heart, nothing radiating to my arms. But when I take a deep breath the pain is worse - feels a bit better when I lay on the floor or when I put a heating pad on it. Still feels like I have a tennis ball that I am lying on, between my shoulder blades.