PHP (Slim) routers don't work after hosting in subdirectory (Using Apache and Ubuntu 16)

I have a few different projects and all of them are set in /var/www/html folder. Each one has its own folder. That’s what I wrote in my virtual host to activate all of them:

<VirtualHost *:80>
    .
    .    
    DocumentRoot /var/www/html/
    .
    .
</VirtualHost>

One of my projects has routes in it - it’s written in PHP using Slim micro framework.

The project is in var/www/html/school folder.

This is my .htaccess file:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [QSA,L]

All of the routers are at routers.php that is required in index.php and they don’t work: could you help me?

That’s the website: http://www.itayperry.com/school/login The login page is the only one that works - I’ve tried adding the word ‘/school’ to every router in my routers.php file but this does’nt work.

I know that if I change my DocumentRoot to /var/www/html/school the project will work perfectly but then all other projects will stop working.