What Causes Armpits And Thigh Boils With Residual Carbuncles?

I get boils and sometimes they turn into carbuncles on my arm pits and inner thighs. Most of the time I can get rid of them myself, every once in a while I have to go to my family doctor to have it lanced. The doctor has taken samples and sent them to the lab and everything comes back clean, still these things keep coming back. The doctor will put me on antibotics (bactrim) which doesn't do anything to help. What causes boils and how can I rid myself ot them permanently.