Hi,
You’re right that costochondritis doesn’t last that long. There a few possibilities left. One is that there could be a fracture which happened when sternum accidentally hits for e.g. steering wheel while driving. To rule it out, an x-ray of the sternal region can be done. Another possibility is a muscular pain which can also last quite long. I think application of some local analgesic creams and warm compresses may help.
I hope that helps. Please do keep me posted. Kind regards.
Check with a chiropractic to see if your ribs are out of alignment or you have some sort of arthritis. When ribs are out of alignment or out of joint, it can be really painful. If the rib next to your heart is out of joint, it can be dangerous. See if a chiropractor can help.