Your pediatrician's CDC growth chart might not be totally appropriate for your breastfed baby, since the percentiles for that chart include babies who were formula fed and those who started solids early. The CDC itself admits that breastfed babies tend to gain weight faster than formula-fed infants in the first three months, and that they tend to weigh less than formula-fed babies from six to twelve months. (That means your baby might not follow one of the curves on the chart that your doctor is used to looking at.)
In 2006, the World Health Organization released a new set of growth charts based on breastfed children around the world. If you are exclusively breastfeeding and delaying the introduction of solid foods until around six months, these charts may be more helpful for assessing your baby’s growth patterns.