Some boils/furuncle have erupted on stomach on waistline. I am in great pain. I have starting taking antibiotic & painkiller. What ointment should I apply on the wound?
And why these occur?

What does your medical practitioner have to say on the matter ?

I agree... if it was me I'd see my doctor.

You should keep your medical questions together. It's slightly possible that they are related.
You should try to keep your boils clean with just gentle soap and water, patting dry carefully, and keeping exposed to air around the house by not wearing pants. A long cotton shirt perhaps.
Were you taking antibiotics from the kidney stone surgery before the boils appeared?