Quoting luvmomyhood:" I'm breastfeeding my LO and having trouble with one of my boobs, for whatever reason it hurt when she ... [snip!] ... I Think I have infection inside my duct or something? I dunno but it hurts. What is it and what can I do? Do I call my OB?"
How long has this been happening? A clogged milk duct should clear up in a few days, it might have turned to mastitis which is an infection. I have had clogged ducts that hurt just like what you described though. Massage that side in hot showers, use heating pads on it, and only nurse of THAT side. You need baby to suck it out.