game lag problem

Hi, 

I bought this alienware 15 two months ago and recently I got a problem with it, everything runs well except every time I play games online, there is game lag every 2 or 3 seconds which makes the game unplayable, this has never happened before and only occurs when I play online games. I'm pretty sure there is no problem with my internet connection as the games on my another laptop running well. I scanned my device, and there was no issue with my hardware, I also tried to reinstall the windows and restore the factory setting several times, but none of these could solve the problem. So any advice on this? 

Thanks