If you change your email address as often as you change your username on this site, Henry, (which seems to be almost weekly!), I'm not surprised if you start getting a bit mixed up!
Gmail accounts don't suddenly disappear (even if you stop using them). If you can remember both the email address and your password all of your mail should still be accessible via the Gmail website (even if you normally get your mail through an email client, such as Outlook Express, Windows Live Mail, Windows 10 mail or Thunderbird or via an app on a mobile device). Simply sign into your Google account here
https://accounts.google.com/ServiceLogin?service=mail&continue=https://mail.google.com/mail/#identifier
and then go to your email.
If you can remember your Gmail address but you've forgotten your password, start here:
https://www.google.com/accounts/recovery/
If you've forgotten your Gmail address the same link might also help you.