Hi webnewbie and welcome to webmasterworld! You say you are already utilizing a login facitlity, so just use that method to protect the admin pages by checking that it is either you or another user with administrative privileges that is logged in and attempting to access the admin page/s. If not, show a blank page or some message or re-direct. Many ways to go about it. You could provide a column in the database for users that have administrative privileges (could even set different levels of accessibility such as 0 through 10, 10 being full privileges, 0 being non-admin etc..) if that were necessary for you to allow some others to have administrative access. But if it is just you, just check that it is you who is logged in.
i already had different levels of accessibility set to determine what navigation bar non members/members/admins see so i just added a few lines of code concerning admin status into the pages i wished to hide to normal users and the problem is solved!