Heavy feeling in right testicle, I found absolutely zero lumps

Hi, 

I was walking home yesterday, when I felt a sharp pain in my right testicle. This quickly faded after thirty seconds, but since then I've had a dull ache/heaving feeling in the testicle. I examined myself for lumps, and found absolutely nothing. I can't really tell if the testicle is swelling, as it doesn't look any different than normal.

Any idea of what this could be? The feeling I'm having is a dull ache, and not a sharp pain or anything like that.