You need to know this for sure ( when you open AVG it will tell you in the top left hand side of the screen ). If it is the Antivirus and you're also running Norton Antivirus it could be part of the "system appears quite slow" problem. Two antivirus apps doesn't give you twice the protection , on the contrary it's almost certain there will be conflict. Best advice is to uninstall one of them.
Which one you ask.........if you let me know which version of Norton you're running , and when your subscription runs out , i can advise.

Can i also ask if you have an Antispyware program installed. ?