hun, this whole baby thing is so hard isn't it.
She could be having a growth spurt or wonder week, it would explain the wanting to feed but falling asleep.

All i can suggest is lots of cuddles and go with the flow, if you can maybe try giving her a bit of tummy time or a baby massage.
A nice warm bath might help if she's got a bit of a tummy ache, just take nice deep breaths and see how she goes.