The lymph nodes, which are located in different parts of the body including the neck and armpit, are a part of the lymphatic system. When a lymph node becomes swollen, it usually indicates infection.The normal size of a lymph node can range from a couple of millimeters to about a centimeter. When there is infection or inflammation somewhere in the body, a lymph node may enlarge and could remain swollen,even after the infection is gone.
Depending of course on what the breast specialist deems appropriate he/she may recommend to just monitor the lymph node growth,prescribe an antibiotic or ordering more investigative tests.
I hope that there is nothing to worry about. :)
Wishing you all the best...