Pumping Breast Milk Help

My water broke at week 28. Baby came at week 31. My baby has been in the NICU for 11 days and will be there until his due date 1-1-17. I am trying to pump as many times a day. I'm not producing a lot of milk. I'm doing everything my lactating nurse taught me. I'm hoping my milk supply will pick up. Any one else experiencing little milk production? Any advice? Could it be because now he would only have been 33 weeks and maybe more will come closer to his due date? Maybe my diabetic medication Metformin has something to do with it.  Very frustrating when I can't supply him enough of my milk.