I have quite thick whiteish vaginal discharge that smells like onion what causes this?

Have MD check: Smell is very subjective and usually limited by the experience of the person doing the smelling. However, it is possible that it does indeed smell like onions. That could be a result of the foods you eat. It could also be that your vaginal flora has one predominant bacteria that creates that odor. However, there is no known vaginal condition that will predispose to an onion smelling discharge.