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The lumps described in your history appear to be enlarged lymph nodes. Other possible causes can be sebaceous cysts, or infected skin glands.
Lymph node enlargement is a very common sign and can cause many people to get stressed and lose their sleep. A few major symptoms and danger signs can help you differentiate very common benign conditions and from those indicating conditions likecancer and chronic diseases.
Symptoms like persistent fever, weight loss, night sweats along with multiple enlarged, painless lymph nodes may indicate chronic conditions like infections or cancer.
With your prior history of abnormal mammogram, It would definitely be important for you to seek a medical examination by your doctor. If all things appear normal, then prescription of antibiotics may be helpful to treat any form of infections, causing the lumps in the armpit.