[Spectato]

Exactly.
It's much more likely to be a service related issue.
"Horrible feelings" aren't really a good basis for troubleshooting a problem.

A better place to start would be to connect your modem and PC directly (ie. No router) and take some speed measurements, compare that to what's happening with router included.
At which point, chances are, you'll probably discover that you're in a congested/over-subscribed area, just the like the rest of us!

Get some help setting up your router's security properly anyway, then you shouldn't need to worry about that.
You may need to take care of some stuff like updating the router's firmware and your operating system's ability to handle the latest security protocols (WPA), depending on how new/old/up-to-date your set-up is.
Or it might be as simple as changing a few settings and entering a few numbers.

There's a gargantuan amount of information out here in WWW land.
You can get started by typing something like "router security' or 'router configuration' into Google!