I think you have a couple of options. If your router is still considerably new, you can probably keep using it. Are you using it via wireless, what kind of router is it?
What you need to do first is to hook your computer directly to your internet provider's modem. If the slow problem continues keep in mind that most internet providers share you speed, so don't be disappointed if one day is slower then the next. This would for sure be within reason.
If the connection does improve, you could reset your router to factory settings, usually with a reset button on the back of the router. After the reset, see if your speed has improved. You can also try upgrading the firmware that might improve performance and fix an issue you might be experiencing.With the information I have asked from you I could probably point you in the right direction. Make sure when entering the model for you router you also list any V.1.x that might be next to the model number.
If you have a wireless router and are connecting your play station and computer via wireless you could also try optimizing your settings. You can change your broadcast radio to channel 10, if you have a router compatible with B-G mixed mode, that would also be another option. Also check for wireless interference or environmental variables.
Like, I said there are many things you can try before you buy a new router.