Well for a start, if products aren't genuine then a lot of the time they will cause some sort of problem or have some sort of defect. If you aren't paying full price for someone's work, but you're still using it without their permission, I see that as massively disrespectful, so that's something I should get off my chest to start with, unless you somehow managed to accidentally land yourself with/pay for a fake. Regardless, get yourself a proper, legitimate OS as soon as possible, and make sure you pay for it.
However I can't say with certainty that that's the cause of your issue - your RAM is also pretty low (ideally you'd have 4GB, but 2GB I'd say is the down-right minimum.) If you have a lot of processes running in the background, all demanding resources at different times then your performance will jump around.
However, I'd have to say that the most likely cause of this issue is heat throttling. To be sure - download HW Monitor and tell us what temperatures your GPU and CPU reach during gaming.
However, you should also check that your drivers are all up-to-date and ensure that your games are all fully patched.
Hope that helps a little,
Good luck
-Nih