Dd is 5 weeks old and for the past 2 days has been really difficult to feed. She cries cos she's hungry takes the bottle in her mouth then starts to spit the milk out and shake her head causin herself to choke but screams when you take the bottle away We've been using multiflow nipples for 3 weeks and she much prefers them to the stage 1 nipples so I don't think that's the problem and nothing else has been changed. Could this be a growth spurt or something? Any ideas?