Hello and hope you are doing well.
The rash could be due to an allergen. The other causes could be due to a fungal infection, atopic dermatitis, contact dermatitis and bacterial infections. Usually there is itching and some amount of inflammation with these conditions. If there is accompanying swelling, redness, discharge and fever it is most probably an infection. But to exactly pin point the pathology you will need to consult your primary care physician who will examine you an may ask for blood tests. If the need arises he may refer you to a dermatologist.
Hope this helped and do keep us posted.