I got the pertussis vaccine a couple days ago and last night noticed a tender, movable, hard, ball just above my collarbone. I remember this happening about 10 yrs ago when I got a flu shot in the same arm, in which I had a soft tissue injury in that shoulder just before the injection. This time the ball is much more sore. Could it be a single lymph node, building immunity? Is this common, and should I see a doctor?