Constipation in newborn

Gigi • 💕married 06/24/2017💕 twins born 02/18/19 Mila & Rudolf at 29 weeks

Does anyone have any tips to help baby poop? The doctor suggested prune concentrate but so far it hasn't helped. My daughter hasn't had a real dirty diaper since friday. She has had a hard ball of poop twice but not an actual bowel movement. Any tips or suggestions? She does have an umbilical hernia so I'm getting a little concerned even though the doctor says it's completely normal