Unstable ping in games

Since one month my ping drops to varations between the 50 and 300 ping in some games and that wasn't there before. I still can't fix it and it has nothing to do with the wifi at home, cuz games that don't run trough Parallels don't have these issues. Also I did all the network fix solutions given on the Parallels website. But still didn't managed to fix it after almost 4 weeks. Does anyone have an idea what I could do next?