The ultrasound should be able to see if there is any lesion. Other causes other than epididymitis would include cancer, a cyst, varicocele or hydrocele - again, these entities should be seen on an ultrasound.
If the ultrasound was negative, other non-scrotal causes can include prostatitis or a groin hernia. A prostate exam can be done to evaluate for any enlargement, as well as imaging with a transrectal ultrasound.
I would suggest a referral to a urologist.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.