I would do a factory reset ONLY as a last resort. First try a battery pull. A battery pull sometimes is more effective that a "restart." But try a battery pull before a factory reset. Remove the battery for a few minutes before you put it back in the phone.
In my experience, Nova launcher is excellent, and I doubt it's the cause of your problem.
But if you are convinced that it might be the cause, simply save Nova launcher's settings to your SD card and then delete it and see if there is any change. If not, reinstall it and import back your old Nova launcher settings.
But a battery pull may solve your problem.
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So I've had my SIII since it came out and have had no big/unfixable problems with it until the last couple of weeks. Apps have been freezing, data is slow and I have to restart it about everyother day. I haven't dropped it and everything is stock.
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