I had very severely blocked ducts last time - breasts were still rock hard after pumping. So after i got my ducts cleared by the LC at KK, i learned to clear them on my own. It will be very painful so you have to bear with the pain.
First you can place a warm towel on your breasts. Massage your breasts in a circular motion, working towards the nipple from the various directions. Continue to massage your breasts (esp the hard parts) as you pump. You shld see milk gushing out and feel the lumps becoming smaller lumps and eventually disappearing. Try this method first. If it doesn't clear up, it's better to seek the help of a LC before you get a full-blown infection.