breastfeeding...help!

So i had my little one on friday at 29w4d. he is doing well however he is in NICU and i have to exclusively pump for at least another 4 weeks. i pumped for the first time about 3 hrs after i had him, and every 2-3 hrs ever since. the most i ever got was 1.5oz out of my right breast and 1oz out of my left. it seems to be going down though, the last few pumps i only got a total of 1oz from both. any suggestions on how to increase supply? should i stay strictly with 2hrs or 3?