1. Can you receive order notification email?

If so, the email address is your login account

You can click "Forgot password" to get a new one

2. Is it possible that you paid the order directly via PayPal without registration?

If so, your PayPal account is the login account

You can click "Forgot password" to get a new one

Or you can search in your email inbox to find out the previous password.

3. Did you use Facebook/Google/Mobile Phone to login before?

If so, the social account is your login account.

You can use the same way to login and you will find your order in the account.