Getting "header already sent" warning, can't find a solution

I created a testimonials page for one of my tutors, from scratch and am including the php to call wordpress in there.

The page is getting a “header already sent” warning.

Warning: Cannot modify header information – headers already sent by (output started at /homepages/19/d#########/htdocs/juantutors/philip-becker-testimonials.php:2) in /homepages/19/d#########/htdocs/juantutors/wp-content/plugins/wassup/wassup.php on line 1994

The code I use to get the modified header is

<?php
require(‘wp-load.php’);
get_header(“philip-becker”);
?>

And the footer is
<?php get_footer(); ?>

A header with the name header-philip-becker.php has been created and does exists. But I am not calling for a header again. I don’t know why I am getting this error.

I need help!