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Looks like you have developed a lesion of Vector dermatitis, also known as Paederus dermatitis
Paederus dermatitis is a peculiar, irritant contact dermatitis
characterized by a sudden onset of red lesions on exposed areas of the body.
The disease is provoked by an insect belonging to the genus Paederus.
Now as in your case the lesion is persisting since few days, you need to apply an antibiotic/steroid combination cream over the lesion twice a day.
Take oral antihistamine like levocetrizine once a day to decrease the swelling
Also you might in addition need a course of oral steroids
or antibiotics according to the skin lesion, so i recommend that you should see a local dermatologist
or physician for the same.
Hope it helps
Wishing you speedy recovery
Dr Geetika Paul