Speaking from experience and in addition to what sqad has said, it really can help to change to all cotton underwear and trousers if you are wearing them and avoid tights, cycling short type things and leggings. Avoid soaps and shower gels in the genital area, plain luke warm water is best.
Take a look at your diet, up the amount of water that you drink and cut out as much sugar as possible, also it may help to cut down/out yeasty foods, beer, bread leavened with yeast, wine, marmite.