Nagging is more like to annoy someone. She keeps nagging me to do this or to go here or to act like this. Grumbling can be a quiet way of complaining without using your words. It just expressive Complaining: you’re actively talking about the issue that is bothering you and usually complaining can turn into nagging because you bother people with the complaints and therefor you grumble in frustration because no one is helping :)

This is what Longman Online Dictionary says about each of these words: Grumble: to keep complaining in an unhappy way Complain: to say that you are annoyed, not satisfied, or unhappy about something or someone Nag: to keep asking someone to do something, or to keep complaining to someone about their behaviour, in an annoying way

Hello Sara. yes, there is a difference. I hardly ever grumble, never nag ...but sure do complain a lot.