i have a mild discomfort right underneath my sternum inner side of bottom right rib....no problems in breathing no cough or cold....just wondering what it may be. it can feel dull like its aching or sometimes like a little sting. only thing i can think of is when i have been playing with my son and throwing him up in the air and catching him, obviously my chest muscles would have been contracting and i may have damaged the cartilage near my sternum, rib a little.