Lags and Stuttering suddenly

I got the game 3 days ago. It was working fine, i played like 15 hours. Then today all of a sudden it started lagging a lot during gameplay. Sometimes it comes to a complete crawl where everything moves in slow mo. I didnt change the graphic settings so I know that's not a problem because it was working perfectly before. I used the Nvidia app to optimize and that didn't work. I tried reducing the graphic setting and that also didn't work. I set them at auto and that still didn't work.