This condition is called blue balls. It's a natural occurrence when you are sexually aroused and there is no ejaculation at the end. It is nothing to worry about, it wont pose any major damage. Just a little pain in the area. The best way to stop this from happening is well after she leaves... bring yourself to ejaculation.

http://en.wikipedia.org/wiki/Blue_balls
^^Read about the condition^^

Oh Thanks.

I have heard of the term before, but I have not fully understood what it meant, till now.

Thanks again.

You are more than welcome. Hopefully from now on your skies will be blue and not your balls