Do you see your doctor regularly for checkups? If so, please mention your breast tenderness to your doctor. If you don’t go for annual checkups, it is not unreasonable to make an appointment.
Do you have an adult in your life you can talk to about this? A mother/sister/aunt/grandma/other?
Do you know how to do breast self exams? I hope that you feel your breasts monthly.
Have you ever been fitted for a bra? I wore the wrong size bra until I was in my 30s. Department and maternity stores usually staff someone who has been trained in measuring women for the proper bra size.
While it is usually completely normal to have some breast tenderness or discomfort, or to have a simple cause such as hormonal changes or improperly fitting bras, it is never wrong to discuss your concerns with your doctor.