Increased sensitivity . Infants neurological systems are immature, their sensory nerves are more responsive when their gut is distended and their pain receptors respond earlier. Normal distension can be perceived as pain by some infants. Their frontal lobe is immature so even though the noxious stimuli has gone the perception remains. Infants have limited ways of responding to discomfort.
Some babies just seem to have been born without an off switch.
Frequency, duration and intensity of symptoms. Other symptoms such as vomiting, diarrhoea and fever to exclude other diagnoses. Pregnancy and delivery. Social history - supports etc. Maternal drugs including smoking and caffeine consumption Examination - both to exclude other pathology and to reassure of normal growth and development.