If I kept erection for longer than 20 mins the pain comes. When I run it also hurts. I think I have prostatitis

Those can be prostatitis symptoms. It is quite possible that you have got a prostatitis.
To diagnose this condition, you should visit local urologyst and do some tests. 
To cure prostatitis, I suggest Diuretic and Anti-inflammatory Pill. It can cure stubborn chronic prostatitis which cannot be cured by Antibiotics. Also it is much safer than antibiotics, there's no side effect with this medicine.                                    
Released in 2011-10-26 09:32:48