Sudden onset of abdominal pain
with an urge to have a bowel movement
and the relief after the act is suggestive of some acute inflammatory
process . It quite possible that you might have eaten something that
was contaminated by bacteria. This is causing gastroenteritis
may even have some slow bleeding from the stomach, Digested blood
comes out black in the stool. If you are not taking Iron supplements
or bismuth compounds, then bleeding in the stomach has to be considered.
Please see a doctor ASAP , so appropriate measures can be taken. In the
meantime , avoid aspirin
type of drugs and stay on bland diet.
If it is food poisoning
, it will clear quickly with time.
Sometimes, you may need an antibiotic therapy.
Wish you well.