You need to state your age first. Right lower belly pain referred to right testicle can have many causes viz, a lower ureteric stone which can often be missed on a ultrasound scan. You may need a CT scan after confirmation from your treating doctor. Other causes of such referred pain may also be picked up, If you are young, I would suggest after clinical examination suggests, you may be asked to do a USG scrotum with Doppler to rule out Varicoceles which often cause such nagging discomfort.