Nazly I express when I can. Its easier if DH is around, but if its just me on my own its a LOT more difficult. I try and do it after each feed when humanly possible but DS is the same in needing to sit up and he's started to want 'playtime' with me. Typically I can do a pump around 3am, 7am before DH goes to work, 5pm when DH get back from work and one around 10pm. During the day, I'm just trying to get one in as and when I can which has been very difficult and I'm finding is getting harder. I can't stress enough, that I could not do it without it being a team enough between me and DH to allow me the time to do it.
I've been winging it as far as amounts go, as I can find NOTHING for babies under a month old. (For older babies this is a useful guide He screams when he's run out though so that roughly how we have worked it out; from the amount he's had and the time to next feed. As long as he's had a 'good' feed he will settle. He gets the same amount each time - its just the length of time between feeds that varies. We have been aiming for 3hrs so if he's wanting more sooner, we've upped the amount. He's currently on about 110 - 120ml (4oz) per feed - the midwife confirmed thats roughly what he should be having now at 4 weeks old.
I bought some breast milk freezer bags and just filled them. In hindsight I wish I'd portioned them better but at the time I thought I would be able to do a lot more bags. But at the time I had no idea how much per feed he would need. If I was to do it now, I'd bag up in 110ml portions.
velvetlilithi the truth is I have no idea how I managed to get a stockpile now really! I simply had an oversupply of milk about two weeks ago so I just stashed. I don't have a magic answer I'm afraid. DS lost weight initially too so I think this explains some of it. He's now gaining weight but it has been slow up to now, though he seems to have put on a fair amount over the last few days from the look of him.
Now I am not quite producing as much as he's eating - I'm losing a small net amount each time now, rather than gaining. I have roughly 400mls in the fridge at any time as my current supply, which works out about 4 feeds worth, so I'm not too far ahead of where you are. Keeping on top of it is HARD work psychically, but probably harder mentally, especially knowing he's eating more than I can make at the moment.
I'm finding I get better pumping sessions at different times of the day too. There are some that I struggle to make a feed, and others I make more, but its roughly balancing out as just under what he's eating over the course of a day. Its tough when I get a 'bad' feed, despite this, as it feels like I've failed somehow. I get more at night and first thing in the morning, with midday pump being the worst.
I'm currently looking for a magic solution to increase supply to match His Lord Hungriness, but I've not found it yet. It does seem like my supply has plateaued off at a pretty constant level now too.