What Causes Discomfort And Tightness In Ribs On Left Side?

I m having some tightness in my ribs on my left side. This is very uncomfortable. I can t wear a bra due to the pressure on my ribs. I had a chest xray last week because I was having difficulty taking a deep breath. That came back OK, but now I feel like my rib cage is tight and sore or bruised under my left arm. Thank you for your help.