C.W.
You should see your doctor as soon as possible. It is possible that you may have mastitis. Mastitis is an infection/inflammation of the glands that produce milk in your breast. In the meantime, if your breast is sore and red, apply ice. If you do not have redness and a fever, apply moist heat. I went through mastitis when my oldest daughter, who is now 21, was a baby. It can be very painful, and if left untreated can spread to other body systems.