3 weeks diarrhea when i get the feeling to go i have to go right then or i cant hold it at all. severe cramps not dairy! today its almost black ?

Persistent diarrhea: It's time to send off a fresh stool specimen, even if it's watery, for culture to check for pathogenic bacteria, parasites or eggs. If you've been taking bismuth antidiarrheal medications, like peptobismol, your stools can turn black. Iron supplements can also cause black stools as can bleeding from the upper gi tract. A physician can check your stool for blood in his/her office. No roughage diet.