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There could be many reasons for this kind of picture. Is he passing stools. It's possible there is gas accumulation due to certain food or an intestinal infection due to possibly worms. The pain could be due to intestinal cramps
. He needs to get his stool examined for parasites. If you are still breast feeding him, continue doing so. Keep him well hydrated. He would also need an ultrasound
to rule out pathology. What kind of diet are you feeding him.