If someone hacked your Facebook account and went through it - you would've have received notification from facebook that your password has been changed.
You can tell if someone went through you account if your settings have been changed, friends are missing, etc. If you did not get a notification from Facebook, I'm sure you are fine.
You can ensure that your password is HARD - a mixture of numbers and letters - so something like 3LilOnes$ - will be considered a hard password because of the mix of number, letters, capital letters and the $....
DO NOT click on things like "see who is checking you out on facebook" - that's a scam.
DO NOT click on chats that say "what the heck were you doing in THIS video"....
That's good that you added the device log in...so now if anyone tries to log in, you will get an e-mail that states device facebook - or what ever you named your computer attempted to log in today at X time - if this is not you, please log into your account...
GOOD LUCK!