She may need to pass gas. Sometimes there is an imbalance of foremilk and hindmilk which causes gassy, fussy babies. Foremilk is the less fatty milk produced at the beginning. Getting too much of this milk is caused by switching the breast too quickly. Hindmilk is formed as the fat globules have time to attach to the milk which is better for their growth and development. Make sure to finish one breast before switching to the other.