You sound very tired and stressed. First off, this will not always be this way. I know, the nights can be long, but you must remember, the years are short. So, hang in there.
There's a book called "The No-Cry Sleep Solution" that many people find helpful. You could try that.
With my 3 yr olds we read stories until one falls asleep, then I lay down with them until the second one falls asleep. It usually works that way, anyway. They only recently began sleeping in their own room. Before that, they were on a mattress on our floor. In the night I have to go comfort one or the other at some point. Maybe your son would be happier in your room.
Maybe he's overstimulated durring the day. Maybe it's about a food thing. That book I mentioned will give you ideas about keeping a diary so you can maybe pinpoint the problems and find a solution. I wish I had a magic solution, but I don't.
It'll get better, I promise. Meanwhile, try to take it lightly. I find when I get all stressed, the kids act worse, but if I try to let it role off, their tantrums and stuff go away faster. I also pray for patience. I don't know if you're religious, but if so, you can draw on that.
Good luck to you and your family.