filter search query post meta

Make sure you are using 'post_type' => 'slug' and not the human readable form of your custom post type. I’m assuming you are but that’s often an issue. Anyway…

Don’t forget the 'meta_key' => 'SORTFIELD', element. This tells WP_Query which meta_key value to sort. Change SORTFIELD to whatever the key’s name is.

The use of ‘meta_query’ requires WP 3.1 or better so make sure you’ve got the latest updates on your site. You can check the Codex for details on WP_Query.

I removed the 'relation' = 'AND', and added 'compare' => 'LIKE', to your elements. This will not ignore fields that are left blank, however. You should write additional PHP to omit fields that are blank so they are ignored. Otherwise you likely will not get any hits if blank fields are left on the form and not in the database. (You never know what people will put into your perfectly planned program that will bring it crashing down!!)

All your values are yes. I don’t get that. I’m assuming you want to take form input and match it against the values in the database. That is what my solution will do…if they select a male doctor they will get only matches of the male gender. Be careful here though! If your choices are female and male you’ll get everything in the database as they will both match a LIKE statement as below. Consider recording male as M and female as F in your database…

You might try this to do what you’re doing above:

$args = array(
	'post_type' => 'Doctors',
	'posts_per_page' => 1000,
	'meta_key' => 'SORTFIELD', // The name of the metakey to orderby
	'orderby' => 'meta_value_num',
	'order' => 'ASC',
	'meta_query' => array(     // This is the problem area! (See below)
		array(
			'key' => 'gender',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
		array(
			'key' => 'age-groups-served',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
		array(
			'key' => 'languages',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
		array(
			'key' => 'location',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
		array(
			'key' => 'specialities',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
		array(
			'key' => 'tests',
			'value' => 'yes',
			'compare' => 'LIKE',
		),
	),
);

You could do something like this:

// Only check these form fields (change the list as needed...)
$fields = array( 'gender', 'age-groups-served', 'languages', 'location', 'specialties', 'tests' );
foreach( $fields as $field ) {
	if( $_REQUEST[$field] != '' ) {
		// We have something to match, otherwise ignore the field...
		$meta_query[] = array(
			'key' => $field,
			'value' => $_REQUEST[$field],  // This is OK, WP_Query will sanitize input!
			'compare' => 'LIKE',
		);
	}
}

And change your $args to this:

$args = array(
	'post_type' => 'Doctors',
	'posts_per_page' => 1000,
	'meta_key' => 'SORTFIELD', // The name of the metakey to orderby
	'orderby' => 'meta_value_num',
	'order' => 'ASC',
	'meta_query' => $meta_query,
);