First question is he diabetic
Looks like tense tender cyst
Needs incision and Drainage
Antibiotics cover may not be enough
Is opposite side axilla normal or not
Next Steps
Consult General surgeon Asap
If antibiotic can't control pain,fever,swelling,send pus for culture sensitivity
Health Tips
Maintain personal hygiene, removal of hair at private parts,don't overuse deodorants, avoid oversweating ,
if found painful swellings over body..don't hesitate to consult at the earliest