How do I find out where my connection problems are?

I'm very frustrated about continuing to lose game after game due to disconnection. I don't see anyone else complaining about it here so the problem must not be with the lichess servers and must be something on my end. Does anyone else have this issue?

I am running Windows 7 SP1, wireless router about 10 feet away, Comcast ISP. Where/how do I begin trying to diagnose this problem?