Google Chrome is fast for 10 mins then becomes significantly slow. Whats the problem?

Pretty straight forward question but ill give you my info that i have got for you. So it doesnt seem to make too much of a difference on how much tabs i have open. Things that become almost impossible to work with are facebook and even typing in google gets very slow and hard. Its not my computer itself. I checked the processor (2.20 GHz) and RAM (4GB) and my internet is running at a nice 12mb/s. I checked google chrome task bar and biggest things are the browser (80000k) and Shockwave plugin (73000) but i watch youtube all the time. This slowness has only just started, so it hasn't always been like this. If it helps im also running Avast internet security. Thanks in advance