Hi Doctor, My Son Is 18 Month Old.stopped Breast Feed

Hi doctor, my son is 18 month old.stopped breast feed recently n strtd giving cows milk.his birth weight was 1.75.he weighd aroubd 7.5 in 16 months.but is physically vry active.im bothered about his weight.also psople saying he looks pale.can i switch to any formula milk.if so suggest one .also sgould i give any multivitamin n iron supplement