A Year And A Half Ago, I Noticed A Spot

A year and a half ago, I noticed a spot on my rib cage (left side) that would radiate pain from time to time. In a few months, there were two more spots on different ribs on my left side ao I saw a doctor and the x-ray didn't show anything.
Since then I have more painful spots and now they are the right side of my ribs as well... A total of eight spots. They never go away but they don't radiate bad pain all the time. However, the pain waves are more frequent.
What could this be?