I Am Concerned. About Three Weeks Ago My Left Testicle

I am concerned. About three weeks ago my left testicle seemed to swell up and was very sensitive to the touch. It seemed like it was three times the size of the right one. After a day or two it settled and had felt maybe 50% bigger then the left ever since. I have read that it is not uncommon for the right on to be bigger but I did not see anywhere that the left one oculd be and swell up like that.