DD is three weeks old, ebf. Most of the time she feeds fine but she keeps having blips where she won't take either breast - she start suckling then break off and cry, or fall asleep after a few sucks. The longest this has lasted has been two days (after which she started feeding again like nothing had been wrong 
). She was weighed just after this and had lost weight again, having started regaining it after the loss after birth. There was another blip last week lasting half a day, and another today which has been going on since 4am. I'm expressing and offering bm in bottles but she's not taking much at all, despite showing all the signs of being hungry. She'll hold the bottle in her mouth but spit most of the milk out. I've tried a cup and a syringe as well but the milk just gets spat out.
We've been to a few breastfeeding groups but none of the HVs know why she might be doing this. And she either sleeps through the groups or feeds fine so they can't see what she's doing when she's refusing it.
As far as I'm aware I'm doing nothing differently; same position, can't pinpoint anything I might be eating that's putting her off. It's like she doesn't want to eat at all, despite being hungry.
Has anyone else had this or have any idea what I can do? She's had very little milk since last night and I don't know how to get her to swallow some. Thanks