How do you tell the difference between a clogged milk duct and mastitis?

Mastitis: Mastitis is another name for a breast infection, and this happens when the plugged duct doesn't clear and gets infected. You will know that you have mastitis because in addition to the symptoms of a plugged duct, you will also feel ill with a fever, or flu-like symptoms. Plugged Milk duct - you may feel pain in your breast, tenderness, occasionally lump is noted.