If you paid for your account with a credit card, or if your payment is showing as having cleared, then your account information has been sent to you via e-mail. If you do not see it, please make sure to check your SPAM or Junk Mail folders.
PayPal, Amazon, and Google sign-ups are often sent to the primary email address on the those accounts, so please make sure that you verify all email addresses attached to the those account to make sure that it didn't get routed to an unexpected email.
For iTunes In-App purchases, accounts would be created under the email address entered in the required box during purchase.
If you still are unable to locate your "p"-username and password please contact support at any time by submitting a ticket on this page