How do i produce enough milk to pump?

I have a 4 week old and im strictly breastfeeding, but i have a problem. Im starting a class and i need to pump for the sitter, but i cant seem to pump and still have enough to feed my little man. If i pump when my milk comes in then i feel like he doesn't get enough to eat, and it takes longer for him to get full. but if i try to pump after he eats, nothing comes out and it just hurts my nipples trying. I don't want to supplement with formula, but idk what else to do. I just started taking fenugreek, so hopefully it will kick in soon. Any tips or suggestions or tricks to help?