Hey eklipse,
it sounds like a case of jock itch. When I was 18, I got a pretty nasty case.
If this is it, wash the area thoroughly twice daily. Then keep the area dry. There are sprays and powder to use over the counter. You can also use corn starch (white powder) which will help dry your skin out also.
You may want to call a doctor to see if he had any other recommendations.
Whatever you do, you want to keep the skin dry. (do not use creams or vaseline which will irrritate the rash further.)
good luck,
tom