Engorgement is when fluid builds up in the breasts, making them sore and painful, possibly even hot. It can also make getting the milk out more difficult, which not only exacerbates the problem, but reduces milk supply if left unchecked. But there are ways to deal with engorgement.
Why it happens
One factor in engorgement is the use of IV fluids during births these days. Especially in the case of a long labor, this fluid has to go somewhere until it can be excreted by the kidneys. One of those places is in the breasts.
Around 3 days postpartum mother's milk "comes in", or begins to be produced in larger quantities. Some degree of increase in size and a feeling of fullness is normal. If baby is not put the breast very often, however, the milk remains in the breast.
What to do about it
If you are still pregnant, you may want to consider forgoing the continuous fluids in labor. If you continue to drink during labor, dehydration shouldn't be an issue.
If you're experiencing engorgement, put the baby to the breast often. Stay in bed and nurse your baby. Let other people take care of meals and everything else. If baby is having trouble latching, because the swelling has caused the nipple to change shape, then try reverse pressure softening first. If baby is really sleepy or not seeming to get much milk out, then get help! A lactation consultant at this point can save a lot of heartache down the road.
Now the Herbal Stuff
One of the oldest and best remedies for engorgement is cabbage leaves. Although they kind of work when put raw in the bra, they work much better if boiled for a few minutes in a small amount of water. You can then put them in a bag in the freezer or fridge for later use. It may be more comfortable to cut out the midrib from the bigger leaves and cut a hole for your nipple. After a feed, put one on each breast. (If they were in the freezer, let them thaw a bit first.) You can replace it when it's no longer cold.
If you don't want to do the cabbage, then cold packs work, too. Don't put them directly on your skin. Some mothers have found that bags of frozen peas work pretty well, since they take the shape of your breast.
Before feeding, remove the cabbage and add moist heat. This gets the milk flowing, and doing some light massage towards the nipple should make it start dripping. Feed the baby, then afterwards continue with the cabbage or cold packs.
An herbal tincture that can help with all the extra fluid is called Cleavers (Galium aparine). It gently encourages lymphatic drainage, which is what you need in your breasts. You can find some here in my store.