W.P.
You are likely producing more milk than your baby is taking in. It can be a very frustrating problem, not just due to mastitis, but many of the babies are a little fussier than average, too.
You could try adding powdered lecithin to your diet. I am second guessing how I spelled it now, but you know what I mean. Sprinkle a bit of it over your dish that you are eating. It will help you to avoid clogged milk ducts. Also look at your bra and see if there are any tight elastic bands touching your breast anywhere. They can be the unrecognized culprit even in the fancy expensive nursing bras. I prefer for my clients to use a sports bra type of design if at all possible.
If you do still get clogged milk ducts, make sure to position yourself and your baby in a way that your baby's chin is pointing towards the painful area when they nurse (this may put you in some strange positions, such as leaning over your baby that lies under you, for example, lol)