Lump on collarbone

Hi, I'm 35 and I've found a lump on the actual bone of my collarbone near my shoulder. It's hard, doesn't move and painless. I happened to notice it in the mirror while getting dressed.
 

I found lots of information about lumps above and below the bone but none about a lump on top of it. 
 

Has anyone had experience of this? I'm trying to get through to the doctor but they're extremely busy so could be a long wait. Any advice would be appreciated.