My apache2/sites-available/mydomain.com.conf file
<VirtualHost *:80>
ServerAdmin webmaster@mydomain.com
ServerName mydomain.com
ServerAlias www.mydomain.com
DocumentRoot /var/www/mydomain
ErrorLog ${APACHELOGDIR}/error.log
CustomLog ${APACHELOGDIR}/access.log combined
</VirtualHost>

When I run the following:
sudo certbot –apache -d mydomain.com -d www.mydomain.com

I get the following output:
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator apache, Installer apache
Cert not yet due for renewal

You have an existing certificate that has exactly the same domains or certificate name you requested and isn’t close to expiry.
(ref: /etc/letsencrypt/renewal/mydomain.com.conf)

What would you like to do?

1: Attempt to reinstall this existing certificate
2: Renew & replace the cert (limit ~5 per 7 days)

Select the appropriate number [1-2] then [enter] (press ‘c’ to cancel): 1
Keeping the existing certificate
No vhost exists with servername or alias of mydomain.com. No vhost was selected. Please specify ServerName or ServerAlias in the Apache config.
No vhost selected

IMPORTANT NOTES:

• Unable to install the certificate
• Congratulations! Your certificate and chain have been saved at: /etc/letsencrypt/live/mydomain.com/fullchain.pem Your key file has been saved at: /etc/letsencrypt/live/mydomain.com/privkey.pem Your cert will expire on 2020-01-11. To obtain a new or tweaked version of this certificate in the future, simply run certbot again with the “certonly” option. To non-interactively renew all of your certificates, run “certbot renew”

What have I done wrong and how can I resolve it?

Thanks