It sounds like a clogged duct. Just try to express it on your own and try some hot compresses. Even after I finished weaning my daughter, I was getting minute amounts of milk for months afterward. I stopped bf almost 2 years ago and I had a clogged duct about a month ago. It happens. It will hurt like hell when you express it, but bear through it and it will clear up much faster if you can get that junk out of there.
If you start getting a fever, or the sore area turns an ugly red with streaks, go to the doc. Other than that, they can't help much. Good luck!