Exclusive breastfeeding is recommended for the first six months of life for healthy infants born at term. Breast milk is the optimal food for infants, and breastfeeding (with complementary foods) may continue for up to two years and beyond. Breastfeeding reduces bowel (gastrointestinal) and respiratory infections. For more information and helpful links on breastfeeding see here.
Routine Vitamin D supplementation of 10 μg = 400 IU/day (20 μg = 800 IU/day in northern communities) is recommended for all breastfed full term infants until the diet provides a sufficient source of Vitamin D (about 1 year of age).
Excellent information from the Canadian Paediatric Society on many topics including breastfeeding, vitamin D supplementation, iron needs, colic, weaning your infant can be found on their website here