Never had this problem myself, as I tend more toward low supply, but have heard around here that Hand expressing helps as pp mentioned, and is less likely to increase supply like pumping will. Using compresses, taking a mild analgesic like ibuprofen or tylenol, or even some recommend putting cold cabbage leaves in your bra.
kellymom.com is a great resource for all types of bf issues, I"m sure there's advice on there.