Hello,
It can be due to contact dermatitis, allergic reaction, viral rash, hives or folliculitis. Please keep the area clean and apply some topical antiseptics. Also wear loose-fitting cotton clothing and use an antibacterial soap or mild soap like dove. Topical caalmine lotion and mild steroid cream also helps. For the itching please take some over the counter antihistaminic like Benadryl or Claritin. In case the symptoms persist then please consult a dermatologist in that case.
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 dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.