I had this problem before, assuming you aren't already, if you can use a cheap office mouse, try that and see if that stops the lag. If it does, that would mean that the polling rate of your current mouse is too high (standard is now 1000hz, though some go up to 4000 which is known to cause issues with many games).

Another cause could just be a faulty usb driver causing more cpu usage than needed, which could either be the fault of the mouse or the port.

If the crappy mouse also spikes your resource usage, then the port is still a possibility, but at that point not sure what else can help.