You have intermittent right groin dull pain coming approximately twice a year and disappearing without any significant treatment. It is not uncommon to have dull aching loin pain on the normal kidney side if you have an absent opposite partner. It is usually explained by compensatory hypertrophy of the single organ, meaning the size of such kidney is significantly larger than the normal kidney. It, however, is unlikely to cause isolated groin pain, as in your case. You must have yourself examined and tested for varicocele or any pathology in your spermatic cord and right scrotum which may cause such dull groin ache.