Can I eat a vegan diet while breastfeeding?

Yes. Vegitarians can certainly breast feed successfully. Those who avoid dairy and eggs along with meats often need to supplement B12 which is found in those products. Those new to the vegan life need good dietary instruction before a pregnancy or breastfeeding. Those who grow up in a vegan family will have learned how to balance thier nutrition which is a must to avoid problems.
Yes. Just make sure you eat plenty of protein and you may want to give your baby supplemental iron drops.