For the past 5 years, I've been having trouble laying down on my left side as it results in a stabbing pain in my chest, behind the left breast. Sometimes the stabbing pain doesn't happen but there is a dull ache. Sometimes throughout the day I get the stabbing pain and breathing makes it worse. Holding my breath for a few seconds makes it go away. Any idea what is wrong? Doctor did EKG and chest xray, everything seemed normal.