alright that happens to me from time to time where when your all sit there for a minute and feel like you really got to go right,i would end up doing what you do but when your sittin there after you go that you still have a strong urg to go this what i did i got so tired of it next just go in go once or twice then leave bath room and i kinow your saying but it still feels like just walk out in few minutes that feeling will have gone ,im telling you it was in my head now ,try it good luck..
My guess is you have a chronic prostate infection, the bacteria travel into your urethra after/during ejaculation and irritate the tissue. Once you finally urinate them all out, the sensation goes away.