Hi, I was just going to start a new topic about this problem when I saw your thread.
I'm a 21 year old male and having been experiencing these shooting pains since I was about 18. I usually get this about once a month but it nearly brings me to my knees; it feels like someone stabbed a knife into my rectum. The pain lasts about 2 seconds and there are no other symptoms that accompany it at the same time.
The reason I came here was because I noticed a new development. I was in the shower tonight and had the same shooting pain that I've had before, but this time it felt like an arrow going through me and I experienced the same severe pain in my lower abdomen.
I tried to show where I felt the pain in this diagram, with the black arrow:
This year I have been experiencing increased urinary infections with at one time, mucous in the urine (this was the most excruciating pain I have ever experienced). There is a burning sensation in the head of my penis and my anus at the same time, so I'm wondering if it's a prostate problem.