Hello!
Any of your seven costochondral junctions may be affected; these are the places where the ribs are attached to the sternum. Cartilage has a very limited blood supply so healing is stretched over a long period of time. I would suggest you to go for an X-ray and rule out any other bony involvement and follow up with an orthopedician for a proper diagnosis. You need to stop lifting of weights and also stop active upper body exercises involving your chest till properly diagnosed and treated. Take intermittent pain killers.
Take care!
Unless you have some pre-existing heart condition, the most likely cause of your trouble is an inflammation of the cartilige around/in between the ribs. It is called costochodritis and it can be very painful, but isn't serious. Advil or other NSAIDs should help with the pain.