Speaking as a random stranger but as one who has suffered this problem myself, your local pharmacy will probably sell cream called Clotrimazole. If not, they will be able to suggest an alternative, probably Canesten.
Moisture is the enemy. You need to make sure you are thoroughly dry after showering. I used to make sure I dried my "nether regions" first, whilst the towel was at its driest. In fact I still do. I also used to blow the area thoroughly dry with a hair drier, set on cool, before putting on the cream. From memory, you need to use the cream for a couple of weeks, twice a day to kill the infection off. I believe it is a form of yeast.
Depending on its extent, it can be helpful to remove pubic hair and clean underwear every day is obvious.
It is a horrible thing and I reached the point after an energetic hike where I was actually bleeding from the area!
Hope this helps.