@whate, NullPointerException offered quality recommendations.
If you are using AVG mainly for it's free service, you have quite a selection of other free offerings. We use Avast! on our Windows 8.1 system. Their free version is available here
https://www.avast.com/en-us/index
Avira also offers a free AV, but there's also a free Giveaway going on right now that's open exclusively to members. It's at the top of the page, but here is the link while it's still active:
http://malwaretips.com/threads/avira-antivirus-pro-2015.41070/
For expert help, you can always turn to our staff whom volunteer with malware removal assistance, by posting a thread here:
http://malwaretips.com/forums/malware-removal-assistance.10/
Each thread is there for your reference but the individual help provided is strictly for the OP (original poster) for their specific problem.
When you have taken the steps and your problem has been left behind, consider using the free sandboxing program, Sandboxie.
A way to understand how a sandbox works keeping changes from being made to your system is how it acts similarly to the way ones home provides shelter by keeping out the heat, rain, and cold. The fact that windows & doors must be opened in order to allow fresh air inside, likewise your browser would also need to be outside of it's protective sandbox in order for desired updates & themes to remain longer than temporarily.
Do update any subscriptions you've chosen for your adblocker, and consider using the free LastPass extension. It works in each of your browsers to securely protect both you and your passwords.
Thank you for sharing your configuration.