Kelly mom is the best resource for breastfeeding help and has excellent information on mastitis, thrush and other causes of breast pain during breastfeeding.

Has lots and lots of information- but I'm not crazy with how it's organized. The text is very small and hard to read. Other than that- seems to offer comprehensive info about the symptoms, causes, and treatments of mastitis.

Really good article that covers all the aspects of mastitis and plugged ducts. Explains the differences, symptoms and treatments. A must read if you have questions about these breast problems.