Welcome to HCM.
Thanks for writing in.
Certain types of infection are not responsive to usual antibiotics. A higher antibiotic course for longer duration can cure the condition.
A proper examination and blood work up would be needed to establish diagnosis.
A pus culture and sensitivity would be needed to decide antibiotic usage.
Consult a qualified dermatologist
for proper diagnosis and treatment.
Hope this helps.
Wishing you good health.