D.C.
I had a similar problem when I stopped nursing, and my lactation consultant advised me to pump to completely empty both breasts, and that did the trick. No more problems after that. It's been over a year since that time, but I think I remember that she said it may be necessary to use warm compresses and massage prior to pumping to loosen the clogged ducts in order to completely empty the breasts.
If you call one of the breastfeeding shops at the Harris hospitals, they could likely offer more advice.