The area you are describing is called the perineum. This is where you can externally palpate your PROSTATE gland.
This COULD be S/S of your prostate swelling up and prostatitis. Are you taking any sort of support supplements? Have you had any difficulty urinating or libido? Just an FYI, your doctor may perform a prostate exam just in case. Just be up front with him and tell him what you are doing.