Hi, Two theories may be applicable in case of having watery stools or diarrhea after sexual intercourse. One is that the prostaglandins in semen, can also cause some gastrointestinal spasms, like we notice in women who have diarrhea at the onset of labor when their cervix is ripening. The other, is that contractions of the pelvic floor are also affecting the muscles around your colon and causing some of the gastrointestinal issues, which could explain why you experience that type of watery stools when you are having a sexual intercourse. During your sexual encounter there inner intestinal muscles getting affected. There is a gastrointestinal spasm which may lead to diarrhea and sometimes severe low back pain that can t be bear. If you suffer from such type of problems repeatedly for long or bother you, then you should consult your family physician first and then the gastroenterologist immediately to find out any underlying cause and then treat it accordingly. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician