So I started to pump at 3 weeks because my milk never came in properly (I had sepsis after birth)
I started to pump around 8-9 times a day (20 mins), including one middle of the night pump (this one is really important as prolactin levels highest). At the beginning I would get about 20-30ml per pump, but now I get around 200-400ml per pump.
At 12 weeks, your supply will regulate and you can start to drop pumps. I'm now on around 3-4 pumps per day.
You don't need to sterilise your pump every time. I only sterilise it once per day, and store it in the fridge when not in use.
To get your supply up, use a hospital grade pump like a spectra or Medela (you can buy cheap on eBay or rent). I'd also invest in a wearable pump (I have a Pipetta) so you can pump out and about. I sometimes do it driving or out for a walk. Makes life much easier.
Also join Exclusively Pumping Mums UK on Facebook.
It's hard but doable. The more you pump, the more your body will produce milk. I started with barely enough for one bottle per day, and now at 5 months I have an oversupply, with 100 bags of milk in the freezer.
You can do it.