Well, I don’t know what is your conf, but you should have a file similar to youdomain.tld.conf in /etc/apache2/sites-enabled/ dir and you should add the part for https, something like this:
<VirtualHost *:443>
DocumentRoot /path/to/your/site/documentroot
ServerName yourdomain.tld
ServerAlias www.yourdomain.tld
SSLEngine on
SSLCertificateFile /etc/letsencrypt/live/yourdomain.tld/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/yourdomain.tld/privkey.pem
Header always set Strict-Transport-Security "max-age=0"
</VirtualHost>
Keep in mind that you should have the certs available in /etc/letsencrypt/live/yourdomain.tld/ or apache will refuse to start.