I agree with the above posting - you should take the necessary test to determine whether there is blood in your motions - or whether the cause could be diet/medicine etc.
If the description of your motions is "foul smelling/black/tarry" then the medical name is MELENA and you may want to look this up on google to search out possible causes. If you have melena then this definitely requires medical advice.
regards
Morecambe
If I'm not mistaken, stools can be black if you have been eating a lot of red meat, have been taking peptobismol, have been taking an iron supplement, or if you have blood in your stool. You should get the three day occult blood stool test done.
Sorry i meant to say left upper abdominal pain