I should have a novice protection but my Stronghold was attacked by another player.

The novice protection is applied to every new player at the time he enters the game for the first time.

The protection expires after 3 days since the first log in, or when a novice player reaches level 30.

Please note that all the protected players are able to attack each-other without any restrictions.

Also, you will lose your protection against any higher level Stronghold on the map, if you attack it.