Having Testicle Pain. Ultrasound Scan Result Came Normal. What Could This Be?

I've been having testicle pain for about 4 months now almost 5 I've been to the doctor atleast 8 times in 1 month had a ultrasound done I also seen a urologist no one doctor can figure out where my pain is coming from I do have a past history of frequently masturbating a lot for about 2yrs now I did it 3 or 4 times in one day and one day about 4-5 months ago when I was masturbating and ejaculated I felt a very harsh pain in my testicles I'm not sure what this is when I had an ultrasound done I had good blood flow in both testicles I don't what's wrong please help.