I've had this on and off since I was around 11 or 12.... Basically sometimes after I masturbate (or occasionaly when I have sex) when I piss afterwards it almost feels like all of the piss doesn't come out and it feels like I need to go for ages afterwards even though nothing is there (it happens worse when I can feel I need to piss whilst masturbating/having sex)... It doesn't hurt to piss but it just feels like you're 'on the edge' the whole time until it eventually goes (usually after drinking lots of water and waiting for a while and pissing everything out)....
For the record I'm a guy. I would think maybe its an STI but the fact I've had it since I was 12 suggests not.... Any ideas what causes it and how I could stop it, I've always been curious (I'm 18 now) but never bothered to find out....