NodeJS working behind Nginx

I have in the same server NodeJS and Nginx running at a time. Nginx takes the requests from "www.example.com" and i want NodeJS to take requests from "api.example.com". I almost got it, i configured Nginx to forward the requests from "api.example.com" to NodeJS (localhost:3000) and certainly it works, except for the requests arrive to NodeJS without any information.

For example, I'm using PassportJS to develop all the logic behind NodeJS. I have something like this:

app.post('/room/create', function(req, res) { console.log(req); } );

And "req", the var who is supposed to store all the information from the request is empty when i access by "api.ismuser.com". But, if i use the public IP:PORT to get NodeJS, it works.

I'm just guessing this is due to Nginx, who is working like a reverse proxy for NodeJS.

I don't know if putting Nginx in front of NodeJS is well done, but it was the only way i found to get working www.ismuser.com and api.ismuser.com with the same public IP.

What can i do?

UPDATED

Nginx.conf:

http {
    passenger_root /home/ubuntu/.rvm/gems/ruby-2.0.0-p195@ism_r3/gems/passenger-4.0.5;
    passenger_ruby /home/ubuntu/.rvm/wrappers/ruby-2.0.0-p195@ism_r3/ruby;

    include       mime.types;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;

    upstream backend {
        server 127.0.0.1:3000;
    }

    server {
        listen 80;
        server_name api.example.com;

        location / {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header Host $http_host;
                proxy_set_header X-NginX-Proxy true;
                proxy_pass http://backend/;
                proxy_redirect off;
        }
    }

    server {
      listen 80;
      server_name www.example.com;
      root /home/ubuntu/ismapi/ism/public;   # <--- be sure to point to 'public'!
      passenger_enabled on;
    }
}