The majority of breast lumps are not concerning, especially at your young age..
Most likely this could be one of many benign lumps like a cyst or a Fibroadenoma .These types of lumps are not cancerous and are commonly found in young people your age, but can also occur in women of any age. The cause of these benign lumps are due to hormonal fluctuations.
Breast cancer is indeed very rare at your age, but anytime you feel a lump in your breast, you should be aware that it is an abnormality and it's always wise to have it checked out by your health care provider who might recommend an Ultrasound if he/she thinks it’s necessary.
Please talk to your mom about it and let her call your doctor for a check- up okay?
Take care ...