I noticed a few days ago that when I inhaled deeply I could see a bump located on my chest where my solarplex is located. It's an uneven bump and not exactly in the center of my chest either. As of late I've been suffering from heartburn quite often, and it's as almost as if i can sense it originating from this mystery bump. When I touch it I feel slight pressure, and If i continue to irratate it It begins to become borderline painfull. It's roughly the size of walnut and when I went to visit a MD he told me it might be build up of fat deposit. I had trouble believing that because I'm not an overweight individual whatsoever. I'm actually standard weight for my height.

Would anyone happen to know what this could be?

Thanks for taking the time to help me out.