Possible reasons may be:
1) hunger cry, but if weight is normal and urine is adequate then less likely
2) change in weather, more likely as since few days session is changed and child may feel uncomfortable
3) colic pain
Next Steps
Make sound environment and comfortable room temperature.
Give adequate and full feeding. Give mother’s milk when child is fully hungry and give it for atleast 25-30 min and then do burping well atleast for 10-15 min each time.
If symptoms persist or weight loss consult pediatrician