But I get no improvement. Please advice me if antibitics is really useless here.

Antibiotics are not completely useless in treating prostatitis, just in somebody, the effect of antibiotics isn't that good. 
Antibiotics sometimes cannot directly work in the prostate gland to cure the lesion and eliminate the symptoms, thus I suggest you to try herbal remedy.
Diuretic and Anti-inflammatory Pill is a completely herbal treatment for prostatitis. You can get cured in three months.                                    
Released in 2011-09-16 15:52:57