I had 4 cases of mastitis before my first baby was even born. Clogged milk ducts all the time, and now that the baby is here I have recurrent mastitis.
One of the women who worked at the birthing center where I gave birth is also a LC, and she just recently went to a conference where BF was discussed, and after some of the advice that she gave me, my cases of mastitis have decreased quite a bit.
Two things that are new lines of thought as far as treating a current inflammation of masitis are these: use only cold compresses, and drain the breast completely after every feeding, even if that means pumping. I guess it has been shown that hot compresses can actually extend the infections. And as far as draining the side with the infection, your body will naturally suck some of your breast milk back up inside when you stop feeding if you don't drain your breast. Since the body is chock full of germs, it can actually further the infection. So, when I have mastitis, and I only have ever had it one side ever, I drain that side with a breast pump if my DC doesn't at every feeding. Between that, rest, liquids, tylenol, cold compresses, and lecithin, I can usually get through a mastitis infection pretty quickly. Different positions help, massaging the mass drains mine really quickly, point the babies chin (if you can) into the mass so the baby is helping to massage it with their chin.
However, since you have had it so many times, I agree with PP to look into some of your daily patterns, and maybe try switching off of underwire bras completely. I can get away with wearing an underwire for a day or two, but after that I usually start to see the beginnings of an infection.
Edited to add - would highly recommend probiotics while going through mastitis as well as about 1500 mg of vitamin c a day. Will help with healing process. ESPECIALLY probiotics if you are prescribed a antibiotic. And if you do get an antibiotic, finish it. So essential.