Internet is so slow, even when I'm connected to it my computer lags.

Hi! Recently my internet has gotten so unbearably slow that when I just even connect to the internet, my whole computer lags and it is rather unbearable. I've done multiple speedtests and hardly does my download speed go past 3 mbps on a 50mbps connection. And the problem is that it's only on this machine. On other machines I get speeds up to 20 mbps (which is still slow on the plan, but considering that they're wireless connections with multiple machines running at once, it's fair.) I can hardly load Youtube videos, photos, and webpages. Most notably when I go and play online games, the lag is just unthinkable. I would like some help with this issue, and here are the specs of my computer and network.

Computer:
Intel Core i5-2400 CPU @ 3.10 GHz
8.00GB RAM
1TB of storage
Windows 7 (64x) installed
ATI Radeon HD 5700 Series 4GB

Network:
ISP: Shaw Communications Inc. on a 50mbps broadband connection plan