I often clean my cookies yet have no problem logging into my account every time.
Do you mean that when you try to log in, the site does not recognise the username/email? Does it give you an "incorrect email or password" message? That shouldn't happen just because you've gotten rid of cookies.
To recover your account if you really can't access it, try
Try clicking on your old username in one of your old posts, which takes you to the profile page, and then click on "Is this your account?" that appears to the right of the user data (this only works if you're not already logged in as another user).
EDIT: Oh, wait, I just got it - you were never registered in the first place! The site just remembered you because of the cookies. Ok that makes more sense. Still, try the account recovery thing above, it might still work.