Object method calling for global $wpdb in header.php

I think the problem might lie in:

$wpdbinfo = $wpdb->get_results("SELECT * FROM bo_mytable WHERE id=3");

$wpdb->get_results() returns an array of objects, yet you are referencing a property on $wpdbinfo (->nameinfo). You’ll either want to loop through the $wpdbinfo array, or if you’re certain you’ll get only a single record (possibly a safe assumption if id is a primary key), you would instead call your query using $wpdb->get_row().