Hope we can help, super!
Ok - first off, call one of the breastfeeding helplines. I am an NCT bfc and our line is
here but there are others.
Secondly, why are you expressing? It is the worst way of i) guaging production and ii) guaging amount of baby's intake. You don't need to do it unless you have an overriding reason to do it (because baby can't suck, for instance).
Thirdly, just feeding him, keeping him skin to skin, and responding to his needs is easier for most mothers than trying desperately to stay ahead or bridging gaps or playing catch up. It is normal and excellent for a 12 day old baby to feed a lot and to object when he is put down to sleep - he is not 'starving' in the evenings, but signalling to you that he wants to be close because your taste, smell, touch and voice are familar and lovely to him Why, when less than 2 weeks ago he was inside you, would he want to be anywhere else but close to you and the food supply?
You don't need to do anything but feed and snuggle, and if you have help and support, your helpers and supporters should be waiting on you and doing all the other jobs.
I take it your ds is healthy, thriving, and showing this with lots of wees, yellow poos and that he has stopped losing weight and is now gaining?
I am sure others will help you here, too