I frequently had blocked ducts when I first started feeding Poppy but they would only last a day or less. The most effective way to unblock a duct was to feed from the engorged breast until it is completely drained. I do not recommend expressing the milk because your body will think you need to produce more milk which could lead to further engorgement. If you are really uncomfortable try to express just a little by hand while waiting for your baby's next feed (the shower is good place to do this). Try to make sure you nurse in different positions to ensure all ducts are emptied. It is also important to fully empty breasts so that your baby drinks the fatty hind milk.
In my next breastfeeding post I will talk about fore milk, hind milk and over supply.