S.
Here are a couple of other ideas that I haven't seen mentioned yet:
When nursing, massage the breast - it helps clear the ducts and prevent clogging....it can also increase milk production. Simply use two fingers and run them from the outer breast down towards the nipple...you can also do this in the shower if you'd like.
Use hot compresses before nursing to help "loosen things up". This sounds silly, but I used my babies diapers for the compress...they are the perfect size and shape. Run them under hot water (as hot as you can comfortably stand) and then just place one over each breast.
Lastly, a word of unrelated advice...but I wish someone had told me this when I was on antibiotics for a plugged duct...I developed thrush after being on antibiotics. So far, my daughter and I have passed it back and forth 3 times. I would recommend taking acidopholous to help keep yeast in check and prevent a case of thrust to begin with.
Good Luck!