I am female 5'4'' and normally around 135-40 lbs. Recently I have lost a few pounds from anxiety and also eating healthy and working out. I just noticed today under my left collarbone and above my left breast closer to the middle of my chest but more on the left side, what feels like a bone. It's hard like a bone but I've just never noticed it before. Is it just my sternum I'm feeling from losing a little bit of weight? It doesn't feel the same on the other side and I've never noticed this before?