php session not saved

in my index.php i have at the top:

                   <?php 
                   session_start(); 
                   if (!isset($_SESSION['login'])) {
                         $_SESSION['login']=0;
                        $_SESSION['username']="";
                   }
                   ?>

i also have <?php include("includes/navbar.php"); ?> and in the navbar file i determine if i should display the logged in version of the nav bar, or the normal visitors version using the following code:

                 <?php 
                 if ($_SESSION['login']==true) { ?>
                             showing logged in version
                 <?php } else { ?>
                             show normal
                  <?php } ?>

when I enter a username and password, the login script is called, the script set's $_SESSION['login']=true; and refreshes back to index.php. Now, thats all fine.. however if I now manually refresh index.php my session is lost and i'm logged out. Also If i go to another page on my website that imports (includes) the navbar, it shows the logged out version of it. So either way, sessions are never saved. I have set session_start() to the very top of my index and profile page before anything else.