I'm 38 weeks and my waters broke 4 days ago. I'm having mild pains and lower backache-am I in labour?

It is quite likely you will go into labour in the next day or two. If not, your obstetrician will normally organise for induction of labour as there is a small risk of baby and you developing an infection (chorio-amnionitis) with the membranes ruptured. Don't listen to old wives tales of 'dry labour'-the waters very often break in early labour anyway, so very many labours are 'dry'.