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.
I am new to the forum so hello everyone. I was diagnosed last September with bilateral breast cancer. In October I had a bilateral lumpectomy and lymph nodes taken on both sides. Half way through my chemo in February I noticed puffiness around my collarbone on both sides. It feels like water retention. I've had scans and MRI done so know it's nothing serious but doesn't change the fact the lumps aren't going down. I am going to speak to my hospital's physio again but thought i would visit this forum as well to see if anyone has been through the same thing and might have some other suggestions or advice. Thank you x