It's a phase. Your little boy probably feels somewhat like you or I would feel upon being plunged into an ice age or apocalypse - everything he knows has gone. It's a new and scary world for him.
He will adapt and learn to exist on the outside, and you will learn to live with him. Those feelings of nostalgia and maybe even sadness for your 'old' life will fade, and you will be able to embrace your new 'normal'. Your little boy will become so very amazing. In just a few months, you will be be blown away by the little person he has become, even if right now you might feel like you couldn't possibly love him any more than you do!
Stick with him. You are his closest, best, most important friend, and the one who is going to see him to the other side. He doesn't know any other way of expressing himself yet, except by crying, but he has lived, listened and slept to the sound of your heart all his life and he loves you.
Your instinct will let you know if he's in pain or not. That cry is like no other - it makes you feel beside yourself. Otherwise, all you can do is hold him close and be there for him. It will pass. His smiles will come in time. His laughter. Cuddles for you. Little games where he will hide his face and then pop up with a cheeky grin, thinking he's really surprised you! The newborn stage is all about survival, for mum and for baby. But gradually it gets SO much better. You're doing great.