Definitions of nag:

• noun:   an old or over-worked horse
• noun:   someone (especially a woman) who annoys people by constantly finding fault
• verb:   remind or urge constantly

  Example: "She nagged to take a vacation"

• verb:   bother persistently with trivial complaints

  Example: "She nags her husband all day long"

• verb:   worry persistently

  Example: "Nagging concerns and doubts"