Milk increase...

Hey breastfeeding mommies! I’m currently two weeks into pumping. My baby girl made her grad appearance at 24 wks (3 months early). I can not breast feed due to the fact of how sensitive she still is. I pump every 3 hours and still haven’t notice a difference in the amount I pump. I’ve not got to hold her yet and I feel that may help my milk really increase but what are some other things I could do? They just started her on 2 mL through tube feeding. So it will be awhile until she eats a little more. Am I not producing enough due to pumping and not actually breast feeding (or even skin to skin time)?