hi..Thanks for your query
The symptoms you mention point towards an acute cause of the lesion.It might be an insect bite / irritant contact dermatitis
to secretion of any insect.It requires oral /topical antibiotic
It is important you visit a dermatologist
to assess the same.You can have oral anti inflammatory
tablets to reduce the pain and swelling till you can visit the doctor.
Hope this is helpful.Take care!