Where is my saves from last month?

@Simplayer1986  Did you start a new save in that time frame, or ever use "save as" to rename the save?  Sims 4 only keeps the last five versions of your save before the current one as backups.  If you want to keep older backups, you need to make them yourself, by copying the save files to another location; or you need to use "save as" rather than "save" periodically, so the game creates a new save slot and leaves the then-current one alone.

You can certainly search your computer for any other saves though.  Open a File Explorer window, click This PC in the left panel, and enter Slot_ in the search field in the upper-right corner.  This will find any other saves that might be floating around.  If you see one you want to check out, click on it and then click the "Open file location" menu button, and you'll jump to where the save is located.  From there, you can move the save back to Documents > Electronic Arts > The Sims 4 > saves, and the game should read it.

You can also check OneDrive for any extra copies of Sims 4 saves.  Here again, move the files back to the proper location, and the game should read them.  Make sure they have the correct format though: Slot_xxxxxxxx.save , where the Xs stand in for an eight-digit hexidecimal (base-16) number, and there are no extra characters in the name.

It's a good idea to immediately make backups of your saves and anything else you don't want to lose as well.  If you don't need them, great, but if you do, you'll be glad you made the effort.