Well, I asked my aunt who was a nurse in the army for some years. She said that it sounds like your body isn't adding the seminal fluid (the white part). Apparently that comes from the prostate while the actual sperm is produced by the testicles. In other words, you might have a prostate problem and should probably be checked. It's not the best of news by any means, but even if the doctor doesn't find anything it's to have a sore butt and good news than be able to sit and have it be a real problem.

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"BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Will he offer me his mouth? BOY: Yes. GIRL: Will he offer me his teeth? BOY: Yes. GIRL: Will he offer me his jaws? BOY: Yes. GIRL: Will he offer me his hunger? BOY: Yes. GIRL: Again, will he offer me his hunger? BOY: Yes! GIRL: Yes. BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Yes. BOY: I bet you say that to all the boys!" -Meatloaf