Why does my new laptop lag sometimes?

[YE04 HLD]

Here are the specifications for my laptop:

Intel 3rd generation dual core i5 processor @ 2.5GHz
6GB of 1600MHz DDR3 RAM
Intel HD 4000 graphics (64MB dedicated lol)
500GB hdd.

It seems to lag a little bit at random times... for example, I will be typing to a friend on Facebook's chat, and my words have a delay before they appear. I am not really doing heavy multitasking at the time either.

This seems quite weird to me, as I know quite a bit about computers (i build them, etc), and I know from my specs that I shouldn't be just lagging on tasks such as Facebook.

Could it be from over heating on the laptop or something?

I am also pretty sure that I don't have a virus, as I've just installed security on my laptop, and scan most of my downloads.

Thanks in advance for any answers given guys/gals, much appreciated