unknown internal bleeding

i have had all kinds of tests done since they found blood in my stools.  I keep losing blood and need 2-3 units of blood every fourth day.  A recent colonoscopy and endoscope showed absolutely nothing as to why i keep losing blood.  A bone marrow test has showed that it is functioning correctly.  I will be going to syracuse for the "camera/capsulte" test and maybe that will show something going on in the bowels.  Is it possible to i am having a female problem, i am 69, never had children, an never been on the pill.  Never had any surgery so have all my female organs.  Might you be able to only suggest any possibilities.  I am thinkng the worst and hoping for the best.  Thank you