If you're exclusively breast-feeding, then you'll need to supplement Vitamin D for your baby; since you're formula feeding him, then you do not need other nutrition supplements until he reaches 6 months old, and then you can start to introduce solid food slowly.
Make sure always feed him with breast milk before supplement with formula.
my son's Pediatric Doctor told me to
supplement him with Tri-Vol-sol for
mixed feeding baby. For pure formula feeded baby,nothing extra is needed.
For pure breast-feed baby, Vitamine D
is needed.