Created a new account by accident or logged into an old account by accident
If your account is totally empty than this is a likely cause, first step to find out if this has happened is to check if you can find any other account by looking at this guide: What email is my account linked to
If you were not able to find any other account using that tactic you can go into friends -> add friends -> search for your own name -> if you found another user that seem to be your account you have most likely logged into the wrong account.
Other Issues