I'm 21 years old and for the last 2 days I've had a dull ache which is only on the back side of my left testicle. It isn't in my groin and I have no lumps or swelling. Its completly centralized to the backside of my testicle. I don't think its my testicle itself which is acheing but the tube on the back side. This hasn't happend before and if it doesn't sound like a cause for alarm I'm not going to bother going to the doctor.
I'd suggest that as you realise you have a pain, and as you've taken the time to register and post on this forum, then I'd also take the time to get it checked by a doc, and be 100% it's nothing bad.