I Have Noticed A Small Pea Size Hard Lump Near

I have noticed a small pea size hard lump near the base of my sternum. I noticed it after a strenuous run whereby I suddenly had a sharp needle type pain near the site of my gall bladder removal via keyhole surgery. My gp is sending me for an X-ray altho a work colleague has given me a ultra sound as I work in a hospital. This showed a dark mass but with not a full circle, the bottom looked attached?