Originally Posted by patc

Could be a cyst, I have one on my right testicle. Its basically a small sac containing liquid, usually formed as the result of minor injury - the body's way of dealing with pus and other "bad stuff" it can't eliminate otherwise. My symptoms are pretty much what you describe - occasional dull ache, can get much more painful if anything puts direct pressure on the cyst itself. Mostly harmless, can be removed surgically if it grows and/or becomes too painful to tolerate. Cysts can be so small that you can't easily detect them, and the pain isn't local enough to pinpoint the location, but an ultrasound will find it/them if that's the problem.

If it is a cyst, you will find some ways of "dressing" (polite term for how you arrange things down there in your shorts) will be pain-free, while others will hurt.