I had the same sensation all the time I had my port in. I was diagnosed with Fibromyalgia in 2000 and had the port late 2002. I thought at the time it must have been placed on one of the tender sites from the fibromyalgia but since then I wonder if it doesn't have to do with the lymph nodes in our chest area.
I suffered through it for four months of chemo. I know this isn't very positive for you but just so you know it probably isn't anything wrong, just one more pain to deal with.