Focus briefly on faces. Baby may startle at loud noises. Some infants are fussy and no cause is ever found. Baby may just need to be held. Try feeding your baby first, then try a pacifier.
Many babies grunt and groan passing even a soft stool.
If the stool is quite hard, this is constipation. This helps to soften bowel movements. If still constipated, give 1 teaspoon of Karo syrup in one bottle a day. This produces a stool in 6-8 hours. If still constipated, call your doctor.