I haven't had sex since the 1st week of pregnancy,if I were to have it now at 34 weeks would it trigger labour?

Not likely. Sex can sometimes help get things going IF your body is ready for labour to begin. Most of the time this would not be the case at just 34 weeks. Many couples enjoy sex right to the end of the pregnancy.

Unless your midwife or doctor recommended not having sex at the end of your pregnancy, for example, as might be the case for someone with a history of premature birth, you are free to enjoy.