My Baby Is 3.5 Months Old,iam Using Formula Milk From

My baby is 3.5 months old,iam using formula milk from day 1 because no bf milk for me,firstly doctors suggests pre nan because of low weight 2kg,from 3rd month onwards we are using lactozen 1,when we start lactozen for 10 days she ok but after that she is suffering with motions may switched to nan pro1 again or continue with lactozen is better which is best for my baby health