nag (CRITICIZE) verb  to criticize or complain repeatedly and annoyingly, often
                          as a way of trying to persuade (someone) to do something 
My mum's always nagging me to get my hair cut. 
The way he keeps on nagging about the smallest things really gets on my nerves.

nagging adj.
a nagging (=complaining and criticizing) voice
nagging (=continuous) doubts/pain

nagging noun [U] 
I can't stand her nagging (=complaining and criticizing) any more.

This page is cited from Cambridge Dictionaries Online. For the original, please visit
http://dictionary.cambridge.org/define.asp?key=nag*1+0