Hi. This could be furuncle/abscess. But if its recurrent we have to rule out chronic condition called hidradenitis suppurativa where pus filled lesions over armpit and groin which lead to sinus and scarring. Right now you can take tab cefixime 200mg twice a day for 5 days. Tab tolpa D for pain morning and night for 3 days.
Next Steps
Best to meet dermatologist. If required they'll drain the pus.
Health Tips
Warm saline soaks for pus filled lesions.