You may be having insect toxic dermatitis
I read your history and saw photograph. There is an erythematous patch with central black necrotic area. It seems that you might be having insect toxic dermatitis. You are not having any symptom like pain or itching..nice.
Do not worry. The lesion might go away after few days to weeks with little treatment. Locally apply antibiotic cream like mupirocin
or sisomycine. Take antibiotic tab for 1 to 2 weeks. Short course of oral steroid
like methyle prednesolone 4 mg thrice a day for 5 days then reduce it one tab every five days and then stop.
Avoid soap bath. You may use dettol
liq. for bath.
I think, you may be improved in few days, still..you consult dermatologist
I hope you got my answer. If you any query,you may ask.
Dr.Ilyas Patel MD