worpdress nginx problem subdomain

think i have a problem. I don’t know where is but i`m looking for solutions.
I have wordpress+nginx+pagespeed, i moved the folder uploads in root and changed with the name “cache”.
i used this command in wp-config:
define( 'UPLOADS', ''.'cache' );
after this i’ve added a subdomain for my site img.stancristina.com and it redirects to cache folder.
cache.stancristina.com and stancristina.com/cache are working, but i want that my files to be visible only with cache.stancristina.com, not stancristina.com/cache.
When i try to make a new article and to upload a file, that file is set primary stancristina.com/cache, not cache.stancristina.com as i wanted.
What i`m wrong?
This is my conf:

server {
listen 80;
server_name stancristina.com www.stancristina.com;
     location / {
                try_files $uri $uri/ =404;
    }
root /srv/stancristina.com;
 index index.php index.html index.htm;

	if (!-e $request_filename) {
	rewrite ^(.*)$ /index.php?q=$1 last;
	rewrite ^/sitemap_index.xml$ /index.php?sitemap=1 last;
	rewrite ^/([^/]+?)-sitemap([0-9]+)?.xml$ /index.php?sitemap=$1&sitemap_n=$2 last;
	break;
	}

       location ~ \.php$ {
            fastcgi_buffers 8 256k;
            fastcgi_buffer_size 128k;
            fastcgi_intercept_errors off;
            include fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_pass unix:/dev/shm/php-fpm-www.sock;

        }

	location ~ "\.pagespeed\.([a-z]\.)?[a-z]{2}\.[^.]{10}\.[^.]+" { add_header "" ""; }
	location ~ "^/ngx_pagespeed_static/" { }
	location ~ "^/ngx_pagespeed_beacon$" { }
	location /ngx_pagespeed_statistics { allow 127.0.0.1; deny all; }
	location /ngx_pagespeed_global_statistics { allow 127.0.0.1; deny all; }
	location /ngx_pagespeed_message { allow 127.0.0.1; deny all; }
	location /pagespeed_console { allow 127.0.0.1; deny all; }
}

#Sub Domain
server {
listen 80;
server_name cache.stancristina.com;
autoindex off;
location / {
root /srv/stancristina.com/cache;
}
}