Comman Z "undo" not working properly / virus advice.

[Restfulnest2020]

Question, in the begging, my "undo" command worked on the last action done. Now it goes back to a wall in a room that was created early on. If I accidently delete something or move something I worked hard to place, I can't undo.

Appreciate advice.

***In searching for more furniture options, I downloaded some software programs that referenced 3D and now my computer has a virus. Just be aware when downloading outside the main website.