Hi - anal/rectal bleeding is never normal. Type in rectal bleeding to google/yahoo in order to find out the possible causes and treatments. Some are more minor - some are more sinister especially for those over 40 years of age.
There is an STD forum on the expert/ask a doctor part of Medhelp and, if you were to post your question there, maybe the consultant could offer professional advice on sexually caused anal bleeding.
Good luck
Morecambe
Yea, never have unprotected sex this way. Never have unprotected sex either way unless both partners are known to be safe. But this way may have a higher risk due to finer skin that can tear.
The reason that the anus bleeds after anal sex is that the tissue tears during sex. It is dangerous in the sense that the tear makes you more susceptible to a variety of STDs.