My Baby Is 38 Days Old, When She Was Born

my baby is 38 days old, when she was born she was 36 weeks old and first 20 days she was in NICU unit due to lungs maturity problem, now she is doing good.
mother feeding is not enough for her and we gave lactodex-LBW for one week and on doctors suggestion we started giving lactogen 1 when ever mother feeding is not enough (30 ml daily twice), but she is vomiting the lactogen 1 milk and she is in taking only mother feeding.
Is there any other/better alternative for lactogen 1 ?