Can't log in

Hello,

All the sudden yesterday facebook logged me out saying my session had expired while I was at an airport. I do not remember my password to log in to my facebook account. I requested code to change password. When it sends the security code for me, I enter it, and it says "You have attempted too many code entries recently. Please try again later." Or "unknown error" So, I just want to know what is going on, and how to I regain access to my facebook account again.