Blocked Duct

What a PITA!

There are lots of things you can do to prevent them. Some things that can cause blocked ducts are wearing underwire (or too small) bras, holding the breast with your fingers when breastfeeding to make space for the baby to breathe (you shouldn't need to do that, or make the "hamburger" any more), use of a nipple shield, any exercise that requires repetitive movements of the upper arm (been playing tennis or doing weights?), cutting short or interrupting feedings...

Otherwise it can generally be an indication that attachment needs to be improved. If you have largeish breasts then sometimes supporting the boob from underneath can help to promote better drainage, you can use a rolled up flannel or small towel if need be.

If you're prone to blocked ducts and there's nothing that you can specifically identify that might be causing it then varying the position you feed in can help. If you usually feed sitting up, trying lying down, if you normally use the cradle hold, try the football hold, etc. If it keeps happening it might be worth going along to a La Leche League meeting and asking them to check your positioning.

Apparently taking Vitamin C supplements, lecithin supplements, making sure you're getting enough fluids and not too much saturated fat in your diet can also help.

As always there's a useful page over on kellymom