N.
I had Cystic Acne and the only thing that worked on me was Accutane. I used it in my late teens/early twenties and it was a miracle drug as far as I was concerned. Nothing topical, and I tried almost everything, came even remotely close to what Accutane did for me. The only side effect I can recall was cotton mouth, but I know it's now considered something of a last resort because of problems others have experienced. Maybe your son is too young and that's why the doctor hasn't recommended it yet? It's been almost 20 years for me so maybe it's not even on the market anymore.
I wish your son good luck. I know how miserable this can be!
Blessings,
N.