A urologist would be the most appropriate next step. It is certainly possible that the pain may be related to the vasectomy. There are also a variety of other causes in the scrotum that you may want to rule out (i.e. cysts, masses, infection).
I would suggst a scrotal ultrasound to evaluate for such masses. If the urology referral is not revealing, you may want to consider other causes of pain that can radiate to the testicle - such as a groin pull, nerve damage, or hernia. A referral to a neurologist may be helpful to evaluate for nerve damage.
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.