What Causes Pain In The Left Rib?

hello, I have this pain below my left breast on the left rib its been a while I can feel the pain when I press on it ,I thought that strained a muscle but just today I felt that there's a swelling like the size of a quarter it only showed when I stretched back ,like a big pimple but its only hurts most when I press on it i feel the pain in my left rib , can you please help