One more thing,this could also be the beginning of a secondary breast development. It is also called thelarche.
It is usually associated with a firm tender lump directly under the nipple, and can be unilateral to begin with.
It signifies the onset of puberty in girls.Tell your mom (or someone very close to you) about it,and I am sure that she will take the appropriate steps to have this problem resolved.
Hi,
You could be having an infection, and need to see your doctor.Don't worry though,this doesn't sound like breast cancer,but infections have to be treated with antibiotics.
From the symptoms,it could be a boil or inflammation of the hair follicles.
keep the area clean and apply some topical antiseptics,until you see your doctor. Also wear loose-fitting cotton clothing and use an antibacterial soap or mild soap like dove. You could also consult a dermatologist who might lance the boil and drain it.
Take care and best wishes.