Hello ? Are you more into breastfeeding or mixtures? My little one is…

Hello ? Are you more into breastfeeding or mixtures? My little one is not latching well to the breast because the milk hasn't come in yet and I am supplementing with breastfeeding plus I have KS and he was fed formula for the first day and night, they brought me formula and he didn't want it! Then 2 times already in the evening they brought a bit to eat, and then at night they brought him to feed but he didn't eat, today he has been on the breast all day, sucking, spitting up, crying again, taking it and going round and round and doesn't sleep properly. Gave him formula and he fell asleep... Maybe he got used to formula? And now the breast isn't