I recently had a baby who is five weeks old. In my third trimester of pregnancy i noticed a thickening under my left arm. My gyneocolgist said that this is common in pregnant women. Now it seems to have spread to under my arm and is a bit painful in the area under my arm but not the thickening. My question is could it be related to the pregnancy and the milk production, or is it something I should be concerned about. I also have firocystic diesese in this breast.