Lalauri89 That's exactly what happened. Everything you've described is save-specific, with the possible exception of achievements. (I don't remember whether they're specific to the save or the user folder.) So if your user data is wiped, you're back at the beginning.
I'm sorry, but if you don't have another backup, there's nothing else you can do here.
As for how this happened, where do you have the game itself installed? You can see the location in the EA App, under Sims 4 > Manage > View properties. If the game is installed into Documents > Electronic Arts, an update could have wiped any data in this Sims 4 folder that aren't part of the game's program files, which of course would include all your user data since that's where it's stored.