First change your .htaccess like this:
RewriteEngine On
## If the request is for a valid directory
RewriteCond %{REQUEST_FILENAME} -d [OR]
## If the request is for a valid file
RewriteCond %{REQUEST_FILENAME} -f [OR]
## don't do anything
RewriteRule ^ - [L]
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/ [R=301,L]
RewriteRule ^([a-zA-Z0-9]*)/?$ index.php?category=$1 [L,QSA]
RewriteRule ^([a-zA-Z0-9]*)/([a-zA-Z0-9]+)/?$ index.php?category=$1&itemId=$2 [L,QSA]
RewriteRule ^login/?$ login.php?category=$1&%{QUERY_STRING} [L,QSA]