cchant86 No, saves should absolutely not grow anywhere near that much with so few changes. And I agree that OneDrive is unlikely to be the problem here. If your entire save file were exactly as you'd left it, that would be a possibility—the idea would be that your newer file was being replaced by a synced older one. But when some changes stick and others do not, it's almost always save corruption.
The number of sims in the save is fine. I've seen cases of more like 10k sims, mostly hidden, and that was pretty clearly the problem for those saves, but below a thousand it shouldn't affect performance.
If you want to do some experimenting, you could repeat the actions that increased the older save's size to 75 MB, to see whether you can reproduce it; then do it again but with Lovestruck disabled. (You could use "save as" so as not to damage this save.) Beyond that, I'm not sure how to diagnose the issue, and to be honest I'd suggest pursuing the thread at AHQ if you get any traction there. Crin may have more ideas and is better at pursuing this kind of issue than I am.
I will say that corrupt lots are a known issue right now, but adding one mostly causes crashing or endless loading, not a save that appears to work until it's time to save. Still, you could test the same lots you've been using in a new save, and also see whether placing them as unfurnished makes a difference.
YoungerSatan How large is this save file? Perhaps you have the same issue with some kind of corruption that's also bloating the save. Please also look for more reasonably-sized backups.