sql that can make right count

Have sqlite table:

orderitems
-id
-item_id
-quantity

I need to count each item_id That is not a problem:

$this->db->query("SELECT item_id,COUNT(item_id) 
                     FROM sh_orderitems 
                     GROUP by item_id 
                     ORDER by COUNT(item_id) DESC LIMIT 5")->fetchAll();

Result is:

 0 => 
array (size=4)
  'item_id' => string '38' (length=2)
  0 => string '38' (length=2)
  'COUNT(item_id)' => string '3' (length=1)
  1 => string '3' (length=1)

But that is not good solution, 'cause: quantity dos't counted. Need something like SELECT item_id,COUNT(item_id)*quantity