Lump on my manubrium

20M, So I have a lump on my manubrium and 2nd rib under my collar bone. It started off over a year ago just small, I went in for a ultrasound on it and they told me it was just cartilage. Ever since then it’s been slowly getting bigger and bigger, now it’s starting to happen on the left side of my chest as well. For my pre-existing medical conditions I have spina bifida occulta, minor scoliosis, rolled forward shoulders, surgery for a pneumothorax, and BFS (benign fascination syndrome). I cant post pictures on here since this page won’t let me, so if someone out there cares can they please message me? The best way to describe the lump is it’s hard in certain spots and soft in some. My girlfriend has noticed that it’s been getting bigger as well, I’m not sure if it’s cartilage hardening, some kind of infection or my worst fear which is lung cancer. I have photos of the lump so if someone can help me more I will send them to you