Graphics Card weird behaviour

Hello,

I have an Ideapad y570 with a Nvidia g555m as a graphics card (I can provide link with info if needed). I have been having some strange issues, where it seems to downclock itself or something similar (maybe to run slower to save battery power, idk...). Maybe it's because of the optimus, but it is really becoming annoying, because games that should run without a problem suddenly lag like there's no tomorrow and then go back to running normally for a few minutes, only to start lagging again... I don't know if anyone else has been having these problems, but it would appreciate it if someone could help me out.