This is probably due to breast tissue or glandular tissue that is left behind. Typically this tissue resides just underneath the nipple. This may require either aggressive liposuction or a small incision is placed between the areola and the skin and the glandular tissue is directly resected.
I would also wait for the swelling to go down from your previous gynecomastia surgery and would not consider any revisions until you are at least 3 to 4 months out from your original gynecomastia surgery.
Congratulations on your surgery and good luck.
J. Timothy Katzen, MD, FACS
Web reference: http://timothykatzenmd.com/breast/breast-reduction-men/