What Causes Vaginal Itching?

i m suffering vaginal itching since last 3-4 months.i consulted a pharmacist,he prescribed 3 vaginal capsules to be inserted.it got better for the first time but when i got the itching for the next time,used the same 3 vaginal capsules(gyno-daktarin)but this time it did not affect.one of my friends suggested to wash vagina using warm water with dettol.is it effective?are there any risks?please do suggest a remedy