Hi runnicnakrun,
just stumbled across your post and thought I should reply.
I was diagnosed in nov 13 and had chemo first then WLE a few weeks ago but I also have a swelling on my collar bone like you (left side) and highlighted this to oncologist on wed as I was concerned, she told me not to worry as I have just had surgery on that side!!!!!! !hmmm.surgery was on opposite side so when I said this to her she said oh well lets have a look and she physically examined my collar bone and neck area and said there is nothing to worry about.
Sorry I cant give you any answers but thought I would share my experience so that your not alone, you should ask to have it checked again if swelling does not go down.
Take care
Wyn x