Dear Julia
Though it is not possible to make a diagnosis without biopsy but in your case I can tell (with 99% surity) that these lumps are part of fibrocystic disease (someting called "ANDI" in medical terminology and depends on hormonal changes in body thats why your lump size cahges at periods). Dont worry it is a benign condition and very common too.
As stated by doctor of cleveland clinic keep awatch on type/ nature/ and cherecter of discharge and lumps.
Best wishes
Dr Tewari
JuliaG13: Many women have some type of nipple discharge or fluid when their breasts are squeezed (or pressed), and its normal. Squeezing the nipple sends message to the brain and the pituitary gland responds by increasing prolactin levels, which in turn produces discharge from the nipple. The discharge can come in a variety of colors - gray, green and brown as well as white. Some women are more prone to more discharge including women on; birth control pills, certain blood pressure medications or on major tranquilizers. These medications increase prolactin levels in the body. There is also certain life periods when a person is more likely to get discharge than others: there may be more discharge at puberty and at menopause than the years in-between.
The time to worry about nipple discharge is when it’s spontaneous (comes out by itself without squeezing), keeps on happening, and is only on one side; or if the discharge is clear and sticky, like an egg white, or bloody. If any of these occur you should have it checked by your doctor.
Many women have breasts that feel lumpy that may feel painful or more pronounced around the time of menstruation. The key to examine breasts is to do this about the same time every month and feel for changes. It would be very unlikely for a 14 year old to develop breast cancer.
Also, the only history of cancer in my family is my great uncle, (not of breast cancer) but i was told that his sister -my nan- gets cysts. I hope this helps! Please reply!