What Does A Small Hard Lump Below The Xiphoid Indicate?

I have a small, hard lump just below & to the side of my xiphoid process. It's about double size of a large pea from what I can tell but there may be more underneath the skin. It is putting pressure on my diaphragm. Doctor's I've seen haven't helped much. I also have a tough time with indigestion. Any 8deas? It's always tender & unless I distract myself, it's a struggle to get a full breath. Thanks in advance.