Pedi says my 6 month has heartburn. She wakes often crying, even when held she squirms and cries. Nursing helps soothe her. What else could it be?

? Teething. While reflux could be one of the causes i wonder if it is from teething since she is comforted with feeding.
Reflux. It could be reflux esophagitis or heartburn as your pedi says. It could also be a kind of food intolerance or allergy. For breastfeeding babies removing milk and other dairy from the mother's diet sometimes helps. If this is a new problem and the baby's stool has become loose/runny it could be an infection. If the stools are very firm, pasty or hard then treat for constipation.