I've been told that you mustn't use clary sage oil until you're actually due as it is meant to bring on contractions. I remember putting a few drops in the bath last time I was due, but it didn't seem to do anything! Have found this on the net:
Clary sage and Jasmine essential oils
Both of these oils can act as a uterine stimulant, which is why they are usually listed as being contra-indicated during pregnancy. This is the reason why many women turn to essential oils for natural induction you could try massaging them into your bump, putting them in a bath, or putting them on a hot towel on your bump. Be warned though, Clary Sage has a very distinctive smell
Hope this helps...