Probably precum but if you have concerns see a urologist.

First of all it's not likely that you have a disease. What you are seeing is semen leakage. Most, but not all, men leak some semen (pre-cum) when they become aroused but before they climax and ejaculate. Almost all men continue to leak semen for a period of time after ejaculation. Some men leak semen almost continually. I'm a leaker myself. Is this a problem? Well, sometimes if I'm going commando and my dick starts to ooze semen I'll have a damp spot on my crotch and it can be a problem. But if I'm cruising a cute guy and he sees my dick getting hard in my pants and is already starting to leak jizz it can be an asset.

its probably u have jsut been horny or had a wank had some pre cum or not long came.. and some stays in the pipe works so to speak so when u have a pee it kinda flushes it out.. its nothing to worry about i dnt think