Help...LO very cranky at night

LO is 6days old. She is well fed & sleeps pretty well during the day. However for the past 2-3nights she starts to be very cranky at about 10pm after feeding. We make sure she is clean, diapers changed, carry her for awhile & try to put her to sleep but she cry like nobody business when we put her to her cot (Sometimes even carrying her doesn't stop her from crying)...help!