Hey,
Ping goes off your connection to the server. Typically when your ping fluctuates, its because of your internet provider. Fluctuating ping is usually because the ISP is overloaded. It has given way too many connections than it can handle. So sometimes at peak hours the connections experience greater ping as the ISP is unable to deliver faster...one common check is that you don't experience it during off peak hours..
I also suggest that you get a ethernet cable (hard wire), and try that. If you have no idea what i'm talking about, then uh. Just don't worry about it, or simply look it up! I hope this helped!
QA;TL