Hello,
It can be due to dermatitis skin. You can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps. You can apply some calamine lotion at the rash as it will help in soothing the skin. Also wear cotton undergarments. If the symptoms are severe then it will be best to consult a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
IMaybe it's just a little yeast growth, which is all "jock itch" is. You could get a tube of jock itch cream and try it. Follow directions.
I forgot to add that if I don't touch down there for a while, it becomes less noticeable, it stops being red but the texture of the skin is the same, sort of dry. Even I don't apply any "friction" for a very long time, as soon as I apply "friction" I see the rashes again.