What Could The Lump Between Breasts Indicate?

i have a small lump in between my breasts, it feels similar to the lumps i get on my neck from time to time, but im more concerned as its close to the breast area. I am 21 so im not in the 'at risk age' but its been there for a few weeks now & hasnt dissapeared compared to the ones that i get on my neck which go away after a week or 2