Hi Infant, when on formula will pass greenish stools. Little straining while passing stools is okay. But the stools he passes should be soft and pasty and never hard. But all tummy related complaints will be less if he is exclusively breast fed. If possible try to put him on breast milk only till 6 months of age. For the gas related stuff and colic- burp him properly after each feeds. As a part of daily massage, you can add specific strokes to the tummy (you may get the details in child care books). You may also give Colicaid drops on SOS basis when he is excessively cranky. In your diet you have to avoid excess milk and cabbage family vegetables. These things might increase the colic in the baby. Colic peaks at around 3 months and then goes off as the intestines mature. Hope I have answered your query. Best wishes and happy parenting.