Internet super slow, for no apparent reason

For the past 4 weeks, my internet has been stupidly slow, and with slow I mean it feels like I'm browsing with dial-up. I first noticed this in my computer, but when I told my roommates, they tought it was just my computer, because everything was fine with theirs. Two weeks later, they also started noticing. But the strange thing is: it is slower on my computer. At first I thought it was because...