Which Type Formula Milk Suitable For Baby With Constipation?

Hi, my baby 1mth 23days old having issue to poo.. Always poo only on 3rd or 4th days. She is drinking Enfamil stage 1 now.. Should I switch her formula? Doctor prescribe probiotics for her and says if does not improve have to switch. Any formula to recommend? Nan or enfamil gentlease milk is better?