Breast skin discoloration

For the last two months I have noticed a discolored area of skin about the size of a half dollar, adjoined to the areola of my left breast.  There is no sensitivity, no lump.  Two nights ago, I had pain in my armpit throughout the night, that was alleviated by sitting up.  So, yesterday I got a mammagram and a sonogram and was given a clean bill of health.  Not knowing what the discoloration is, I am still disconcerted.  I have read several other posts regarding this similar occurance, but have read no explaination.  Anyone know what causes this? I am 43, mother of 3 who just stopped breastfeeding an infant a year ago.  Any thoughts on this would be appreciated.

[Cleveland Clinic]

Dear myjosiejones, Skin on the breast like skin on other areas of the body is subject to various conditions including discoloration.   Without ability to see and evaluate it is difficult to say what this is.  An area of skin discoloration is not a usual sign associated with breast cancer.