Hi becca.
Along with Swede's suggestion, I'm also wondering if you have downloaded anything from the Sims 3 Exchange. Maybe clothing or a house? Sometimes there are odd things in those downloads that can cause the distortion that we see on your Sims. You said you don't have any mods, but what about third party custom content? This would be clothing, hairstyles, etc. that you download from a website other than the official Sims 3 site. These downloads are very bad about causing distortion. If you have any of this stuff, I'd recommend that you remove it from your game.
Also, check to see if your computer meets all of the specifications for running the game properly. Many times, a computer's graphics card isn't sufficient to run the game the way it's supposed to. I've got a pretty nice and powerful desktop computer and I had to upgrade the graphics card for the game to run right.
The last thing I can suggest is reinstalling the game. It would be best if you don't try to keep your existing game files because that's where the problems might be. It's a good idea to reinstall the game periodically anyway just to give it a fresh start from time to time. Carl, Metro, and I normally reinstall the game when an expansion pack or a stuff pack is released. It's just a good time to wipe everything clean and get updated for all the new content.
I hope that something here helps with your problem. Keep us posted on how it goes.