bottle in breast-fed

My LO is two weeks and two days old and she is a bottle and breast fed I would like to only be breast-feeding her but I definitely wasn't getting enough because she'd be screaming crying and once she got a little bit of formula she would stop and go to sleep but now I'm giving her the little bit of formula to supplement with the breastmilk but she's getting constipated really often has any other moms given their newborn a little bit of prune or apple juice with water I was told that it is safe. No rude commmments please 😊 & hoping to get my breast pump in the next week up my supply and quit formula