Congratulations on the birth of your little one. I have been in your position - I had my baby 12 weeks ago at 27 weeks. I have managed to express the whole 12 weeks, and I'm now breastfeeding her, so it can be done!
Like you, I really struggled to produce anything at the start. I was struggling to get the 0.5ml that she needed every 3 hours when she was first born! After the first day or two I was getting 4ml. The midwife put me on the electric pump even before I had produced anything at all from the right breast and I was on it for about 45 minutes with nothing happening other than me getting very sore.
Your milk will come in properly in the next day or two, the only advice I can give is to keep at it with the expressing but do it by hand until your milk is properly in, like someone else (25 weeker maybe?!) said. It's apparently important to express at least once through the night as this does something for increasing your supply. Make sure you drink plenty water, and there is a tablet called domperidone that you can get if all else fails. although I didn't end up needing that.
If you can stick with the 3 hourly expressing it honestly will get better, and once you are allowed a cuddle with your baby, if you express straight after it will really help - all of a sudden I got 100ml after my first cuddle with Sophie - but she was 3 weeks old by that point.
Did your midwife show you how to massage your breasts to get the milk flowing? That really helps. I went to a breastfeeding support group in the neonatal unit a couple of times - it's run by a lady from La Leche - and they advised to stop and massage again after expressing for a few minutes. They also said - this probably looks really funny and best done in a room on your own! - to bend over and shake your breasts after massaging them! I never tried that but they said it really works!
You will find your supply increases the more you express and you may experience variations in the amount you express over the weeks. I was panicking last week because I was back to just producing 20ml each time - but then I started breastfeeding Sophie, and it started to increase. We got her home yesterday and it was my first day of breastfeeding her for all her feeds, and this morning when I woke up I was like Jordan lol! When I went to start feeding her this morning she just looked at me and the milk started pouring out before she even started sucking, I'm not kidding!! I'm hoping it regulates itself as we get used to the feeding - the nurses assured me I will start to produce the amount she needs and it will regulate itself.
If you have any questions, pm me. Good luck! xxxxx