Growing lump in neck

I am a 40 yr old mother of 3.
I've had a lump in my neck on the right side, above where my thyroid would be (it was removed for cancer in '94) for over a year which has at least doubled it's size since I first found it. It isn't painful, but I noticed when my little boy grabbed my neck while we were wrestling, it really caused a lot of discomfort. I also have trouble breathing when I walk up even a few stairs and it's quite difficult to catch my breath after that.
I do have a history of cancer and eosiniphilic granuloma, but would really like to hear that there are other common causes of these symptoms.
Thanks for any help.