Hello. This could be in relation to bacterial infection of the skin in that area due to excessive sweating and friction leading to a condition called folliculitis. Other reasons such as fungal or allergic reaction also have to be ruled out. Firstly you should consult with your dermatologist so that appropriate medication can be prescribed. Avoid wearing tight clothes and also determine whether the soap you are using right now suits your skin. Avoid scratching and take over the counter antihistamine medication. Keep washing regularly with only water and keep the area dry. Hope this will help. Regards.