Hi crinrict!
Yes, it was that there was no "lastexepction" files showing up in the documents folder. I was concerned it was the whole game and not just my save file.
However, I took your advice about creating a new save file and it works now! I believe it was something in my build that glitched the saves somehow, despite not using any mods. The save worked until I tried to put the same house on the lot at its current state and it gave me the same issue. I have since deleted that house and started over with absolutely no issues saving yet.
I appreciate the advice! Thank you again!