I am doing a mini cut at the moment but unfortunatly I have this when I'm lean too always had it since I was 15 and was never over weight growing up
If its there when your lean, its probably gyno. You not having a lump is probably because its puberty related gyno.
A good gyno doc could take care of that easily. If it bothers you that bad, have it fixed. Usually runs about $6500 USD