|The Windows firewall is not an antivirus like the other two and should be left on at all times unless you have an alternative firewall.|
Normally you have only one antivirus in case they conflict, although I doubt Windows Defender will cause any issues. You can always temporarily disable real time checking in Windows Defender to see if it helps, like this:
Open Windows Defender from tray icon (right click) and you will see it in the Settings tab. Just uncheck it. If it is not the culprit put it back on again.
MalwareBytes, already mentioned, is good at finding issues that antivirus programs miss. You can get it here (green button top right):
Let us know how you get on and if MalwareBytes finds anything paste the log on here.
Always pop back and let us know the outcome - thanks