$link_to = $_SESSION not working

I am trying to have my users go to there own profile page. I am using this code in php to do it.

session_start();
$link_to = $_SESSION['username']."_page.php";
header("Location: $link_to");

The problem is that the result is bringing me to a page that looks like this.

http://www.domainname.com/_page.php.

It doesnt put the username infront of the _page

What am I doing wrong and is there another way to get this accomplished?

Thanks.