If you've had plugged ducts before and this feels worse, it sounds like you may have mastitis. IF it is, you will need antibiotics to clear it (it's ok for nursing mom's). I have had 2 bouts of mastitis and a couple of plugged ducts so I can appreciate what you are going through.
if it is actually showing red on the outside of your breast that I would think, again, that it's mastitis.
Please see your doctor so that they can decide if you need antibiotics or not. The faster they are in you, the faster the relief.... adn the relief comes fairly quickly.