Baby 5 months still drinking very little — normal?

my baby just turned 5 months old. he born premature 1 month and drink 60-115 ml every 3-4 hours and only 6-7 hours when sleep at night. but never refuses milk. I always wait him hungry only give him drink . you need check baby growth chart (weight, height) to see whether develop as per normal rate. probably need to change type of milk maybe not suitable for baby.