Welcome and thanks for your question
I would be pleased to help you with your Question
It could be either an infection called Furuncle
, or Erythema Multiforme
( a part of Crohn's disease)
It would be best diagnosed on visual examination .
Depending on the condition the treatment would be either an antibiotic based to steroid
Please do visit a Dermatologist
for further opinion .
Thanks and take care