What is it, is it bad, and should i be worried?

ok here it is. A little bit above my collarbone under the skin is a little bump (or little m, maybe? idk the technical names for this..) Its about the size of my finger nail. It hasnt always been there but its been there for about a year. It doesnt hurt, and there isnt another one above my other collarbone. I'm not really worried about it, more curious than anything. But should i be worried? When i run my fingers across my neck i can feel it move, like a little pebble under the surface of my skin. But what is it?