From past few months I can see black pepper like particles in stool, and undigested food in that also, And now from about 2 months colour of stool is dark brownish black like stool and still I can see undigested food and seed like particles and black pepper like things with very foul smell from stool and now stomach pain also started and its continuous pain in stomach specially in half of lower part of abdomen, I visited different doctors many times in this span of time and they said me to do ultrasound test but even ultrasound is normal, what to do next? Is this a symptoms of any type of cancer or any other serious disease? Please give your expert advice.