Nipple piercing heals better and easier if it's made with barbell. Ring moves a lot more than straight barbell, and this can irritate the wound. Rotating ring also brings unwanted bacteria to the wound.
Healing process takes 3 to 12 months. In that time wound can constantly excrete interstitial fluid. This doesn't mean that the wound has infection, it means that the piercing wound is healing and takes some time.
Sometimes healing process takes more time for ladies and also excrete more fluid. It's recommended to remove the piecing when you get pregnant. Don't use lace bra, for to avoid jewelry get stuck with lace.
Wash the piercing twice a day with warm water.