my best deduction would be that since it is does not cross the blood-brain barrier for mama, and if the very few side effects that it may have are not bothering you, i would keep taking it, since there are no known side effects tot eh breastfed child of a mother taking domperidone. (unlike reglan, which i would advise moms to wean off of as soon as they feel their milk supply is adequate, since it has multiple known side effects that are pretty common.).
***disclaimer~ this is not medical advice~ just one mama to another

for actual medical advice regarding this, see a doctor that is willing to work well with a lc