My boyfriend has diabetes and he is constantly suffering from posthitis. his doctor prescribed topical creams and it doesn't seem to be working.

Prostatitis?: If you mean prostatitis and this is being treated with topical creams would suggest that your bf get a second opinion. Have him see the best urologist in your area (ask other doctors for recommendations).

Better sugar control: Better blood sugar control, hygiene and prescription for Diflucan (fluconazole) would help.

See below: Posthitis, or balanoposthitis, is an inflammation of the head of the penis or "glans", typically caused by a chemical irritation or a fungus. If he is not circumcised, this can usually solve the problem. It can be managed with topical steroids, but if its a fungal infection, he needs an antifungal medicine. Good luck!