I Have A Hard Lump That Feels Like Bone A

I have a hard lump that feels like bone a little bigger then a pea above my xiphoid but at the bottom of my sternum slightly to the left maybe a cm from the center. It feels like part of my bone and it doesn't move. When I press it , it hurts maybe 2-10 on the pain scale so not aweful but also is discomferting when I expand my chest( like if I puff it out trying to look big) I noticed it a few days ago and it hasn't changed for better or worse. I've been searching online but haven't found anything on what I'm experiencing