It is possible to use essential oils to make douches to treat vaginal thrush infections.  The best way is to dilute the oil in vodka (2 drops of essential oil to a 5ml teasoon of vodka) and then add the mixture to a pint of cooled (just below blood temperature) boiled water.

Many large chemists sell douch equipment however it is not a good idea to use this method constantly as it interferes with the vaginas own secretion and if sympoms continue consult your doctor.

Here is an interesting article for more information.

Vaginal Douching - To Douche or Not to Douche