It seems that you may be having insect toxic dermatitis
There may be bite of some insect unknowingly.
There is development of erythematous papular and vesicular round lesion with gradually developing necrotic ulcer in the center.
There is initially itching followed by pain. There may be secondary bacterial infection.
Take antihistaminics like levocetirizine
to relieve itching.
Antibiotics,anti inflammatory drugs and steroids
in tappering dose may be taken.
Apply antibiotic cream.
Apply soap bath. Take bath with dettol
You may be alright in few days.
I hope you got my answer.
Dr. Ilyas Patel MD