Yuck! If you are still having breast pain and feel like you have the flu (or been hit by a truck) yup, mastitis :-(
It helps to get milk moving to loosen the clog, and nursing in different positions helps "get at" different ducts. I literally laid DD on the bed and crouched over her, lowering myself until my nipple was in her mouth. It hurt like heck but i think it helped.
Stay hydrated. I have been told that mastitis can happen as a result if a clogged duct or also doing too much. Take care of yourself!