859janie Try playing in a clean user folder. Move the entire Sims 3 folder out of Documents > Electronic Arts and onto your desktop. When you launch the game, a clean folder will spawn with no content. (Your saves and other content will be intact in the folder you've moved but temporarily unread by the game.) Don't add anything to the new folder yet; just start a new save and see whether the problem happens.
If the new save is fine, you can copy your sim from the old Sims 3 folder to the new one. The file for the "household" you saved would be inside Library, and it wouldn't have an obvious name, but you could copy over everything in Library if you wanted, or just find the file with a time stamp corresponding to whenever you created this sim.