Could she be crying because she needs something? Eg milk or diaper change or is she feeling cold/hot? Or could she be gassy?
Babies go through growth spurts at certain ages. During those spurts which lasts roughly a week, they get hungry more often. Growth spurts usually take place at 7 days, 3 wks, 6 wks, 3 mths, 4 mths, 6 mths and 9 mths.