Cure for constipation for a 3 year old?

my daughter has constipation since 6 month ago.this is the list of things that i ' ve tried: fruits,fiber,water, liquid paraffin (5ml bd), 2 days before i gave her so much prune but she didn't have any feeling of pooping yet!she cant take milk of magnesia too.i did everything for this problem!!! like all kind of suppositories too.