php force page to reload includes

I am developing a website with php jquery Sass bootstrap etc etc

The way I have it set up, I have one index page that has all of the includes for the header, css files and js files, and different pages are loaded with a SESSION variable that tells the index what page to include (and there is also a helper page that reads GET variables and stores them in the session and redirects back to the index).

I noticed that if I add a new include or change an include on the index page I have to close the tab and open it again in a new one in order for that to take effect. It's not a huge deal, but its wasting a lot of my time trying to find errors that don't exist.

Anyone have any ideas of what would be causing this?\

EDIT: I realized that this problem occurs with every change I make to the css files (but not the php files) and logging out of my site and logging back in will show the changes, so I don't actually have to close the page. It seems like an issue with the SESSION. I also thought it might have to do with the header(location:) command since your not supposed to use it with in the body of html, so i switched it to echo '<script type="text/javascript">window.location.replace();</script>'; and that didn't fix it either. Also added:

header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Cache-Control: no-cache");
header("Pragma: no-cache");

to my header.php file and that didn't solve it either.