My 2 month old baby is having watery stool with lots of farts and sour smell. since sunday morning but only 3 big stools and lots of smear kind.

Infant diarrhea: It sounds like your infant may have gastroenteritis, an intestinal infection. Most cases are viral, but, if there is blood in the stool, this could indicate either a bacterial infection or a milk protein allergy. Continued watery stools can quickly lead to dehydration in infants. You should definitely have the baby seen by the pediatrician as soon as possible.