19 Year Old Male. Black Dots And Blood In Stool.

19 year old male. Black dots and blood in stool. Stomach ache. Constipation. All symptoms are sporadic. Comes and goes. Has seen a doctor numerous times and has been told nothing is wrong and just keep an eye on it. Is somewhat of a hypochondriac and is thoroughly convinced he has cancer. The reason I am asking is that my daughter is dating him and we do not want to be insensitive however we are relatively certain this is psychological.