I had to express when my DS was born 6 weeks prem, I found that once my milk came in I was getting quite a large amount in the early days, using the hospital's machine. I bought a Medulla Swing when I had to leave my DS in the SCN and I was d/c home. It was around this time we also began to BF. DS had nasograstric feeds for the first week. So I would BF one side and express from the others. I would get anything from 60ml in the morning to 10 mls by the evening. After DS came home I continued with this regime for a short while, but had a reasonal supply in the freezer, so I started to ween myself from it. I still occasionally express, but after a dismal attempt a few weeks back I started to feel expressing was not working anymore. The suck of my DS is so much stronger than the machine. On Wed morning I chucked a hissy fit as DS was being unsettled and between him and my cat I was not getting much sleep, I left him in bed with DH (DS prompltly went to sleep) I got up to express and managed to get about 120ml.
I think the time before, where I had low supply was becasue I wasn't drinking enough water. I have since made an effort to increase my water intake. I have also found I don't get as much milk from expressing as to what I'm sure DS is getting from BF.
Also your bub is still quite small so you probably don't have a large supply yet.

I wash my bottles and pump in hot soapy water and sterilise ever day or so.

I recommend you express with every feed, cool it all in the fridge before combining them, then freeze. You may only get 1 feed per day, but you will slowly build up a supply.