I've had this problem since i was 14. Unfortunately its permanent for me (the nerve damage was, and so the problem is)

it does cause a LOT of pain if i'm not careful. There's a simple way to deal with it though.

Just urinate immediately after sex.

It takes up to 15 minutes for the semen to 'harden' in the bladder. if you pee right after sex, it comes out much smoother without any pain at all. I hope that is helpful to someone.