My first DC (now 11!) was a forceps delivery, and he cried all the time - total exhausting nightmare. I think it was the forceps birth, and he was perhaps in pain. Someone suggested cranial osteopathy, but I was too exhausted to sort it out. Seeing the suggestions above reminded me. With hindsight, really wished I'd done it. Can you get your hv, OH, mother, anyone, to sort out an appointment for your DS?
To get through this period, imagine you're climbing Everest. Don't expect to have a jolly happy time - it's hard work. However, when you're at the top, and can see the view, it's worth it. You just have to hang on in there.
Re expressing, I used to drink a pint of water, have a biscuit, look at the baby rather than the pump, and imagine I was feeding him. As it's a reflex, it's a matter of getting your mind in the right place. It's a skill, and you can't expect to master it at once, so don't get disheartened. Lots of people never manage it, and my OH gave my DS the odd bottle of formula to get through.
Just remember, we all empathise and have been through it. I personally found it the worst point (just about in my life!), and things only get better.