Firstly, not washing your vagina with soap does not increase your risk of having infection. When they say don't wash your vagina with soap, it means that don't wash the inner part where penis or sex toy goes into and where menstruation or child come out from.
The vagina is self cleansing, the discharge women have are ways of the vagina cleansing itself and maintaining a healthy state until its becomes compromised.
The vulva on the other hand which is the external part you can see- the skin or fold that entails clitoris, labia majora, and minora can be washed properly with plain water without fear of smelling or having an infection. If you must wash with soap, use a simple toilet soap and not necessarily everyday. But don't ever dip your fingers inside your vagina or douch claiming you are cleaning it, doing that can alter the pH, cause an imbalance of the natural bacteria in the vagina which can result to an infection.