This resource is one that really helped us out with our little one's food sensitivities:
Dairy and other Food Sensitivities in Breastfed Babies.
The source also explains:
"Some babies with allergies or food sensitivities exhibit fussy nursing behavior. Often when there is a sensitivity to something in mom's diet, baby will come to the breast hungry but when she tastes/smells something in the milk that will cause her GI distress, she pulls off, bats her head back and forth, etc. Sensitivities to foods in mom's diet are rare. If this is the problem, you will most likely notice other symptoms, such as excessive spitting up or vomiting, colic, diarrhea, rash, persistent congestion or runny nose, or excessive gas."
Do you have any symptoms of oversupply? See here:
Forceful Let-down (Milk Ejection Reflex) & Oversupply
Overactive let down is often associated with too much milk (oversupply).
Also look into the possibilty of reflux.
Let us know how things progress for you!