Hello and thanks for the query
The Protrusion can be a cartilage
or a hard tissue swelling or bump. As per your description it is painful and getting large so you need to be investigate for this. You have already done X-ray and further you can go sonography
of chest and CT scan
. Needle aspiration test is the another option you can go for but discuss it with your doctor before going for any investigation.
Hope you got your answer to the query.