Occasionally, especially when I have not ejaculated for a few days, immediately after I do I have a feeling that I am having a cramp in my rectum that feels like the area of my prostate. This is whether I am masturbating or having intercourse with my wife, if has been more than 4 days or so since I came. Doesn't happen everytime, and the feeling lasts anywhere from a minute to 10 minutes. Also, nothing has been in my rectum, lol.

Has anyone else ever experienced this or have any idea what it might be?