Sometimes when you are on your period your breasts firm up or feel sore. It is natural for the body because that usually means they are growing
Female breasts stop growing and developing by age 18.
your fat
because they are growing
Genetics
yes they do
The size of your breasts are determined by DNA. When you gain weight all you are adding is fat to your breasts and this has been shown to be a contributing factor in some breast cancers. Your breasts will change when you become pregnant. There is nothing you can do, except surgery, to change the size of your breasts. Some breast exercises will firm them, but not add to size. Get a good bra that also helps.
because theyre not done growing
because they are growing.
no
Are they growing?
There growing, or your hormones are at a high level.