First, I'd recommend going to a doctor to see if they have some medicated cream that is a bit stronger and can address the rashes you are seeing now before soccer season starts. Second- during the season make sure you keep the area very clean and look into alternative fabrics to wear for your undergarments- they make several types of clothing that are designed to pull the moisture away from your skin, rather than let it sit- you can go to your local sporting goods store and find several options (for example, Under Armor is one brand that makes several options). Right after your games and practices- shower and put on clean clothing. You may even try small amounts of powder in the areas that sweat tends to gather.