No breastfeeding

Alana

Before my son was born I had planned on breastfeeding had great milk production before and after birth, but he has never wanted to breastfeed, we switched to formula because he wasn’t eating enough and therefore not gaining enough, but now he is super constipated, he has been formula fed since 6 days old now is 4 weeks old and still won’t poo unless he has had prune juice, any advice? He is gaining great now he has gained almost 3 lbs since going to formula