You don't actually need to know your username. Your email address can be used in its place to login. But if you have forgotten your password, use the "Request new password" feature. Enter the email address that goes with your IECA account (if that doesn't work try your other email addresses--you may have registered with one of them instead). You will be sent an email with instructions to use a one-time link to login. Use that soon or it will expire. Once you get logged in, you will see your username in the upper left corner of the page.
Suggestion: have your web browser remember your login for the site.
Second suggestion: us a password keeper app to securely store your passwords and other sensitive information.