Incision and Drainage of pus from the breast helps to relieve of the pain and swelling. Pus formation can be due to multiple reasons. In lactating women, the pus formation could be due to stagnation of the milk in the breast. If the breast tissue suffer an injury due to compression or chest fall, tissues get damaged.
Since the breast is a sensitive organ, with rich nerve and blood supply, pus formation may take longer time than tissue at other parts of the body.
Your doctor will usually drain, and fill the drained area with a medicine soaked gauze bandage to promote granulation and healing of the tissue. Healing should usually happen in 3 to 6 weeks' time. This depends on the how deep was the wound and how intense was the pus formation.
In food, eat more protein rich diet. Protein is required for rebuilding of the cells and thus make a normal structure. Reduce on high carbs as this can lead to slowing of the digestion process. You can also increase on butters and cheese as fat tissue is also required for proper formation of the breast tissue.