The signs and symptoms usually appear suddenly and they include:

Breast tenderness or warmth to the touch
General malaise or feeling ill
Swelling of the breast
Pain or a burning sensation continuously or while breast-feeding
Skin redness, often in a wedge-shaped pattern
Fever of 101 F (38.3 C) or greater
The affected breast can then start to appear lumpy and red.Some women may also experience flu-like symptoms such as:

Aches
Shivering and chills
Feeling anxious or stressed
FatigueContact should be made with a health care provider with special breastfeeding competence as soon as the patient recognizes the combination of signs and symptoms. Most of the women first experience the flu-like symptoms and just after they may notice a sore red area on the breast. Also, women should seek medical care if they notice any abnormal discharge from the nipples, if  breast pain is making it difficult to function each day, or they have prolonged, unexplained breast pain. Breast abscess
A breast abscess is a collection of pus that develops in the breast with various causes. During lactation, breast abscess develops only rarely, most sources cite about 0.4–0.5% of breastfeeding women. Known risk factors are age over 30, primiparous and late delivery. No correlation was found with smoking status; however, this may be in part because far fewer smoking women choose to breastfeed. Antibiotics were not shown effective in prevention of lactation abscess but are useful to treat a secondary infection (see the section on the treatment of breast abscess in this article).
It is of tremendous economic importance for the dairy industry, and it is also of concern for public health. The same considerations apply to mastitis in sheep and goats and other milk-producing females. It is also of economic importance in the sow, but, in this species, it is not related to public health. In other domestic females (queen, mare,  etc. ), it is more an individual illness dealt with by veterinary practitioners. References
External links

Mastitis on mayoclinic.com
Australian Breastfeeding Association