Probably want to sort out whether it's your wired access or your wireless access that's the problem, first.
What happens when you connect your work laptop (or any of the other devices) to another of the router's LAN ports? Similar performance to your main PC? Or, still degraded? If the latter, then it's not your wireless...
If performance is similar, then look to your wireless side for issues. Grab an app like Wifi Analyzer
for your phone. See if there's other routers using the same channels as yours. If so, change your channels. See if the problem goes away.