Cystic Acne

Does anyone have a treatment for cystic acne they recommend? I had no acne as a teenager, now that I'm 20 I've started developing cystic acne on my chin. I'm on the pill and they last month round, so it doesn't seem to be hormonal. I have a clarisonic face brush, exfoliate, use clay masks, and have a topical antibiotic prescribed by my dermatologist but it doesn't work. I've tried oral antibiotics but after I finish them they quickly return. I also eat an extremely clean diet due to medical reasons.