Mastitis or a Clogged Duct?

Nichole
One of my breasts is SO SORE. My nipple hurts as well, it is hard and so sore with sharp pains while the breast pain extends into almost the armpit. That side of my breast is rock hard. I'm in so much pain and was thinking of going to the dr tomorrow, but was curious how the dr would differentiate between a clogged duct or if it's more?