Breast Feeding

Newborn premature son is 8 days old, I had him at 36 weeks, 3days & he will latch to me sometimes but not a lot. he wants the bottle more than anything & I'm pumping each time he gets the bottle but I'm afraid for my milk supply because the pumps don't empty my breasts like he will. he's my second child, I breastfed my daughter until she was 9months old. I try different nursing positions for him but he gets aggravated & wants the bottle because it flows quicker. Any advice?