Keep having reoccurring boils on face. not staph, diabetes, or herpes. what could be the cause? dermatologist keeps giving me bactrim (sulfamethoxazole and trimethoprim) and trimethoprim

Multiple possibiliti: There are any number of things that could be the underlying cause. However, infection is the most likely, other skin diseases or conditions can also be the cause. A dermatologist or plastic surgeon can help determine this. If you are unsure you can always seek a second opinion.

Cystic acne?: Sounds like the dermatologist is treating you for cystic acne. Perhaps you need a second opinion or you might try seeing an aesthetician if the antibiotic is not working.