3 week old who is EBF has suddenly started vomiting up the vast proportion of each feed. She then cries, grizzles, strains and hits out with her arms and legs until I feed her again. Then she vomits that up too. We are passing stretches of 8 hours at a time where I am feeding, she's vomiting, I am comforting, she's crying and grizzling, I'm feeding again, she's vomiting again. She gets exhausted and sleeps for 40 mins, then wakes up crying again.
Any idea what this could be?