Pumping help

I had my baby the 23rd of this month my milk just came in the 25 or 26th I started pumping that very night my baby is in the nicu so I'm trying to get a good supply before he comes home I was planning formula feeding him until recently so now I have no clue what I am doing. I try pumping every 3 hours 15 mins on each side but I barely make 20 mls by the end of the day and night I'll have as much as 3 ounces if I'm lucky so I'm kind of stuck and getting frustrated with it. Any advice would be greatly appreciated ive also tried massages and compresses.