Pain in the area between the penis and rectum when sitting is most often associated with inflammation of the prostate, or prostatitis. It may feel like you are sitting on a golf ball or other hard object. Conditions such as infection, an underlying medical condition or pinched nerve can cause this type of pain.
Prostatitis can have both bacterial and non-bacterial causes. Acute -- temporary -- and chronic -- long-lasting -- bacterial infection occurs as a result of back flow of urine leaking into the prostate ducts. Bacterial prostatitis is not a sexually transmitted disease, nor is it contagious. Whether the infection is acute or chronic, inflammation of the prostate results in tenderness and swelling that can cause prostate pain, or pain in the perineum. Sitting as a means of coping with prostate pain will typically make symptoms worse.
Non-bacterial prostatitis or chronic pelvic pain syndrome is the most common type of prostatitis. The exact causes of the non-bacterial infections are unknown. Potential causes include infection by organisms such as chlamydia that are not usually found in the prostate, inflammation due to an immune system response to an injury or previous infections, or muscle spasms in the pelvis that irritate the prostate. All of these can cause perineal tenderness or discomfort that can be aggravated by prolonged sitting or activities -- such as bicycling -- that put pressure on the perineum.
The pudenal nerve supplies the genitals in both men and women, as well as the lower rectum and the perineum. A pinched or compressed pudenal nerve can cause pain in the area of the prostate. Damage to this nerve can be caused by prolonged pressure -- such as sitting on a bicycle seat, trauma, surgery or tumors. Pain typically increases with sitting and may be relieved with standing.