One of the big factors in women stopping breastfeeding seems to be blocked ducts, and then often mastitis.
A friend just had a bout of full-blown antibiotic-requiring mastitis, so I emailed her all the advice I could think of which I had ever encountered. I think if women were given good advice about blocked ducts, lots of them would feed for much longer than they do.
Please add further anti-blockage ideas in the comments...
Sometimes one can clear the blockage by pushing the milk through with a hand while baby is suckling (pushing from the armpit past the place where it hurts all the way to the nipple, or from the torso all the way, if it's a blockage right on the front. They often seem to be in the armpit though).
Avoid wearing a tight bra, or anything else which constricts the flesh on or around the breasts. A tight t-shirt can be enough to induce a blocked duct for some women.
It often helps to have the bottom of the baby's mouth (the bit which does the real sucking) on the same side of the breast as the blockage. Prepare for some odd contortions...
It might help to lie the baby on their back, and have mama go on hands and knees over baby while breastfeeding to clear the block. It looks very odd but the gravity helps. Mooing is optional.
If your breast is hurting, the moment important thing you have to do on that day is to clear that blockage. Hot towels, cabbage leaves, lots of nursing on that side, maybe try a breastpump - whatever it takes. If you go to sleep with it still blocked, you risk infection and fever.
The most outrageous advice I have heard (but also, anecdotally, the most effective) is: your baby is not the only person in the house with a mouth. I've often heard of people enlisting the help of their nursing toddlers to clear a baby-induced blockage - they suck so hard that it takes seconds. And if there aren't any of those available, a co-parent is also an option. They'll save you 5 days of illness for a few moments of cultural dissonance, in the complete privacy of their own home. And remember, they can always spit not swallow if the whole idea is utterly revolting to them (though the breastmilk would probably do their immune system the world of good ;-b )