I had this issue when my baby was six weeks old. I found that nursing him in different positions helped. I normally used the cradle position or the laying down position (at night). When the duct was plugged, I used a football hold position. I would also begin nursing him on the side when the duct was plugged since he seemed to suck very hard on the first breast offered. I also took really warm showers and massaged. Heating pad at night helped as well. It went away after five days finally. It was so painful! Good luck and I hope that it clears up for you!
I second the football hold position! It worked a charm with my second. With my first, I pumped most of the time and still got clogged ducts ughhhhh (so much for pumps draining fully... nothing drains your boobs out better than a baby!).