Breast lumps are very concerning. I would recommend that you see your primary care doctor
to have this evaluated.
Breast cancer is unfortunately a fairly common condition. One in eight women will become afflicted with breast cancer in their lifetimes. Especially in people with a family history of breast cancer, this is always a concern. Fortunately, it is somewhat rare in young girls your age. In addition, while possible, it is actually very rare for pain to be caused by cancer. Cancer often painless. Therefore, while this needs to be evaluated, there are many reasons to think this is not cancer.
There are many others causes of painful breast lesions. The most common cause is functional breast cysts. Women often have breast pain and lumps (caused by cysts) that vary with their menstrual cycle. This is because the breast tissue responds the the changes in estrogen and progesterone levels that occur during a menstrual cycle. These can be treated, including use of oral contraceptive pills. Other common causes include fat necrosis in which the fat of the breast is injured and calcified. Other causes to rule out are infections (mastitis) which can cause pain.
I would recommend that you discuss this with your doctor. While not likely cancer, this deserve evaluation.