Thanks for writing to us.
Without looking at the lesion, it would be difficult to diagnose it. But it could be an insect bite, eczema, bruise etc.
Right now continue taking Benadryl
and apply steroid
cream mixed in calamine
lotion over the rash two times in a day. Follow the prescription for five days but if lesion does not seem to respond, please meet a dermatologist
Hope this helped.