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I understand that it might be scary to go to the doctor. However, if you notice any changes in your breasts or anything unusual, you really need to talk with your doctor about it. Here is where you can learn about common signs & symptoms of breast cancer: http://www.nationalbreastcancer.org/About-Breast-Cancer/Symptoms.aspx.
Doctors will usually start performing clinical breast exams when you go in for regular checkups at about age 20. They are checking for abnormalities in your breasts and it's really not that scary. If you have concerns about it, though, the doctor may teach you how to do a breast self-exam. Here is where you can learn about how to do a breast self-exam: http://www.nationalbreastcancer.org/About-Breast-Cancer/Breast-Self-Exam.aspx.
At the age of 16, you really don't need to worry too much, but it is very important that you pay attention to any changes in your breast and consult your doctor if you have concerns.