Guest Orders will never show in your Purchase History because you were a 'guest' on the site at the time.
If you used the same email to create that Guest Order as you did to create the account you now posted with, you may have to change your email address associated with this account, log out, clear your browser history, restart your computer, and try to follow the details of your Guest Order from the confirmation email sent to you. Otherwise, you may just land in an endless loop of error messages.
Or, if you used paypal, follow-up on your missing order there. Find the order in your Account Activity and send a message to the seller to ask for tracking.