This is normal for many girls and mostly caused by the sweat and friction between the two. I would go see your family doctor to get it double checked to make sure it is nothing more serious and to get a medicated cream to relieve it.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.