Mastitis is a bear. Have you been to a lactation specialist? Have you read Total Nutrition for Breast-feeding Mothers by Betty Kamen, Ph. D., and Si Kamen?
There are ways to prevent mastitis. Specifically YOU HAVE TO GET ENOUGH REST =). Also make sure to nurse using a number of positions, never the same position over and over again. Wear comfortable bras. Watch out for situations that might cause you to burn through your energy. This next bit of advice might sound silly, but it makes all the difference. Make sure you can replenish yourself (recover fully and that includes proper self-care through nursing too) and if others are challenging or complicating your replenishing make sure you learn how to stand up for yourself, set limits, and can set that standard respectfully.
Yeast infections can happen inside the breast. Awful, I know. You sound like you have the symptoms for it. Antibiotics cause yeast to overgrow. Eat lots of yogurt and have your doctor write a prescription to rid you of yeast. There are ointments and what not. Usually if your chest is infected, then the baby, you, and your spouse will be too.
In the future if you feel like your body is possibly coming down with mastitis, 1st STOP EVERYTHING, 2nd make homemade cayenne pepper capsules and garlic powder capsules (take at least 3 of each, they are natural antibiotics and can stop the infection from invading the surrounding tissues as long as you do not have a fever yet-if you have a fever it is too late, you will have to get antibiotics), 3rd use a breast pump, 4th ice the area for 20 minutes after you pump, and 5th SLEEP!!! You can beat mastitis to the finish line this way. But you have to sleep. Growth hormone can do a lot for you to recover you when you sleep, but you HAVE to sleep.
A little more info...
Soon after I had my first daughter, a nurse taught me about the garlic and the cayenne pepper technique. If you can find capsules at a health food store all you need to do next is find powdered garlic and powdered cayenne pepper. Then you fill the capsules yourself. I have also found raw garlic to work in an emergency, but it really doesn't taste as good, as you can imagine. Hopefully someone at the health food store can walk you through some techniques of filling the capsules without making a monster of a mess. It does take some finesse. I usually take 3 of the cayenne and 5 of the garlic. Then a nap. If I wake up and still feel at risk a couple hours later, I will do the routine again. Warning: don't take the capsules on an empty stomach and be aware you may smell like a garlic factory for a day or two. It is worth it to avoid over exposure to antibiotics though. My daughter kept nursing just fine though it.
Hopefully you are one of those that can pace yourself well. For me it has been a bit of a jungle to cross. If you can avoid mastitis through rotating nursing positions and getting adequate sleep-that is best. But if you find yourself riding on the brink of mastitis at times, the "natural antibiotic properties of garlic and cayenne pepper plus sleep" technique does wonders.
by the way, my comment about icing for 20 minutes after you pump...
Forgive me if this is old news =). Icing lets your body know the extra nursing you did is not something to add to the daily routine. You don't want to inadvertantly increase your milk supply. It is a basic rule of thumb, ice tells your chest to slow down, warmth tells your chest to speed up. If you ice just after you pump during mastitis, it will tell your body to just keep at a constant rate for milk production. Hopefully you can avoid the typical overproduction that accompanies pumping during mastitis that so many others suffer through before things finally balance back out to normal.