I concur, your account seems to have been hacked. Someone must have had your login information. (email and password)
Click on the below link. You can find all the information to help you recover your hacked Facebook account:
If your Facebook page is presently online for everyone to see, while the recovery process is going on, do not try to create another account. If you do, it will be disabled and eventually you may never get to go on Facebook anymore.
Facebook has recognized you as the owner of your original account, but someone must have changed the password.
Let me know and good luck