Possible Clues:

• Rival at work?
• It's painfully laborious when the vet goes by rail like this
• To drag wearily round museum is hard work
• Painful or laborious effort, like childbirth
• Old word for pangs of childbirth
• Toil - anguish
• Labour, making path round State
• Labour has got a number in tow
• Route through which Virginia finds work
• Virginia in series in labour