How can i tell if its my lungs or back that hurt?

Other symptoms?: Usually, conditions that cause pains from the lungs, or from the lining surrounding the lungs, would cause respiratory symptoms - cough, shortness of breath, wheezing - while those causing back pains would cause more postural symptoms - worse when sitting, or walking, or lying down, or bending over. That's one way to tell, but a directed physical examination by a doctor would be ideal.