Hi, Hope things are improving for you. Lansinoh is fab and you should notice a difference soon. I used to apply it before and after every feed or expressing session. Rest really does help. If you can take to your bed between feeds and just get a nap, the next feed will be better.
I didn't have a prem baby but she was a very lazy feeder and didn't gain for ages. My milk never "came in" so it was hard work for me to build up my supply.
I used to rugby ball hold her to feed one side and express off the other at each feed. (well not if I was out!) The idea is that you trick your boobs into thinking you've got twins! This way you get more milk expressed coz you've got all the letdown hormones working from feeding your baby on the other side. I could still switch sides coz you never express out all the milk that a baby can get to.
Also the 3am feed was my prime time for milk production, I used to be able to get about 4x the amount I got the rest of the day. Eventually I could get enough for DH to give DD a bottle of EBM at bedtime, as a NEVER had enough milk for her at this time of day, and I could get a headstart on sleep, thus helping the night feeds.
Other than that the midwifes recommended drinking whenever you're feeding ie fluid in-fluid out. and spreading your calorie consumption throughout the whole day, as you are now working 24-7. I managed to BF DD for 10 months and was only told about fenugreek tablets in the last month or so, I think they make a difference but don't know if its a placebo effect. Either way I will be using them if I have another.
Good luck, it does get better, I think the first few weeks are hell for most of us.