Hello. I Have Noticed For The Past 2 Months I

Hello. I have noticed for the past 2 months I have something that feels like a mass/lump or swollen muscle right below the breast bone/sternum in the center. I am only aware of it sometimes. It does not hurt and does not move. I tend to have slight shortness of breath at times too, I'm not sure if it's related. What might this be? I'd appreciate some feedback. Thank you.