For the yoghurt to have any effect, it HAS to be inserted. Externally will be of little benefit. Next time you’re on your period, dip an unused tampon in LIVE natural yogurt and insert into your vagina or use a syringe (without the needle!)

Natural live yogurt can be used in two ways to deal with thrush; eating it and/or inserting it into your vagina. The key is not the yogurt itself but the bacteria, lactobacillus acidophilus, in the yogurt. This helps the body maintain, or regain, its natural pH level and keeps yeast under control.

Some studies have claimed eating yogurt may help keep yeast levels low throughout the body, but particularly in the stomach and intestines. Because candida in the bowel can easily make its way to the vulva and vagina, keeping your digestive system clear of thrush may help prevent vaginal thrush.

Edit
So then just use Canesten.
References :
RN