I exclusively pumped for DS until he was 6 weeks. I pumped every time he fed (day and night) to keeps supply up. I can't remember how much I used to get, but after the first week I didn't supplement with formula so was pumping as much as he was eating.
Some women struggle with pumping though and can only get a few drops.
DS is mostly on bm now, but we still have to supplement with a couple of bottles a day. Hopefully in a few weeks he'll be on just bm. I'm not pumping throughout the night as I need any sleep I can get atm! I pump just before I go to bed and as soon as I wake up, and get about double in the morning what I normally get.