Left Side Testicular Pain....again?

I am a 21 yr old healthy male who oiver the past couple days has had a dull pain in my left testicle. Now I would be more worried anout this if it never happened before, but it has. Two yrs ago around the same time I had teh same pain in the left testicle. I went for an ultrasound and everything turned out to be fine, no lumps just a small varicle, a very small cyst 0.5cm i think and a build up of fluid that the doctor told me not to worry about. The pain then went away. Last yr around christmas the pain came back again. I went for another ultrasound and again it showed everything was the same as last yr the pain went away again. Now I am having the same pain again. Its not a sharp pain its just the same thing?? what can this be?? should I be worried about it since I had it twice before and it was nothing, what should I do??