I have had a left middle back ache for 4 months and keep thinking it's my lung. It's there every day and my left shoulder hurts too. I had my bloods done twice and oxygen levels checked and tapped and listened to and all ok. If it was muscular why now am i feeling chesty and bringing loads of green phlegm up every day too. I am trying to be rational but i can't stop worrying it's my lung.