If I exit the game, everything disappears. Please help!

Okay, here's the problem:
Everything that I have created except for my Sim families and the lots they are "assigned" to disappears if I exit the game: my community lots, all the resident lots/houses I've built, etc. Anything that doesn't come standard with the game disappears as if it were never there. I need help.

Thanks!

Have you tried opening your Origin app, right clicking on the Sims 4 cover and doing a game repair? I do it quite regularly to be honest as with continual development the game does suffer some annoying and random glitches. Also go into the Sims 4 folder on your computer, open the cache file and delete anything lingering in there as it's unnecessary rubbish that can cause problems. Also be careful if you're downloading any mods online, as a lot of them require certain EPs and don't always tell you. I hope you get up and running smoothly again without losing everything!