Hi My Four Year Old Daughter Has Been Having Constipation

Hi My four year old daughter has been having constipation issues since birth we have always talked to her doctors about this problem when she does go its really hard and compacted and hurts her. the doc said to give her as many fiber gummies as it takes to get her to go we were giving her 6 a day not working. went back then they put her on miralax a half cap every 2 hours in juice still not working.I don't know what else to do. Rickie W