Preemie mom, low milk supply help!

Ana
I had my baby boy 2 weeks ago at 30weeks. He has a feeding tube since he is still too small to start breastfeeding so I've been pumping since he was born. It took about 4 days for my milk to come in and since then my supply slowly increased for the next couple of days and then it just kinda plateaued, however it is not much at all. 
I pump every 3 - 4 hours during the day and every 4 - 5 hours during the night (so about 6 or 7 times daily and for about 20 min per session) my total output for the day is only about 1.5oz. I massage during pumping and do manual expression after. A friend recommended I take Fenugreek pills so I started taking that 2 days ago but haven't seen a change yet. I'm guessing I need to pump more often so I will try that, especially at night, any other tips or advice?