Awful frame rates

[Pchronos]

I have a strange problem:

I have horrible fps but whenever I change the video options like SSAO or depth of field it "fixes" itself and I can play normally. The thing is it doesn't matter if I turn it ON or OFF, whenever I change my settings it fixes until I reboot the game or something, then the next time I play the game it gets horrible fps, and I have to go back to video options to turn ON/OFF one of those things so I can play normally.
I have to do it whenever I load the game for the first time.

What could it be??