i have been having pain in my right testicle for about 6 weeks now. I went to my doctor and he told me to get an ultra sound.I did this and nothing came up. The pain started on March 14, the last time i had unpotected sex was in early january, my doctor said it is not neccesary to get an STD check due to the fact i have no symptoms besides the pain, my testicles are not swollen and the timing of my unprotected sex, what could be the cause of this pain