OK, here's a real reply to this question that will help anyone who is reading this who has this issue and actually wants advice to solve this. Reason is usually that you are actually dehydrated and your penis muscle did not have hydration when you jerked it. The result is a 1 hour or so discomfort - it doesn't actually hurt but it almost feels like you have a bladder infection for the first hour, a feeling of always needing to pee. I used to just sit on toilet and read something for an hour and problem subsided - but good news - if you don't have an hour you can do this next fix - Jerk off again. That's right - jerk off again. Because your muscle was dehydrated you sort of left it hanging in ejaculation contraction state. Find something awesome to jerk it to, get hard again, and finish the job. The next time you ejaculate the discomfort will subside. The muscle will contract again and in doing so it will release from the current state. Its weird jerking off right after you did the deed - but it works. Give it 10 mins before you jack off second time - this is a proven solution - This advice is Gold - what are you waiting for?
It's muscle soreness from over ejaculation. Give it a rest for a day or two and you'll be fine