She could be going through a growth spurt. I alsways found my boys would sleep and feed wgen they were going through a growth spurt and they needed to put all of their energy into growing. If ound 6 weeks and 12 weeks to be the biggest period of change in their patterns of feeding and sleeping.

My 5 month old still struggles to stay awake longer than and hour and a half at a time, although he stays awake for most of the morning now!