Can a baby diagnosed with GERD also have infant colic?

GERD/Colic. Yes, the discomfort from esophagitis associated with gerd can be difficult to distinguish from the presumed discomfort of intestinal peristalsis associated with having bm's and passing flatus which is traditionally called colic.
Hard to say. The old research definition of colic was fussing for 3 hrs/d at least 3 days/wk in the first 3 months of life with NO KNOWN CAUSE. Brazelton often cited the baseline fussiness of infancy in normal babies as a behavioral milestone but colic exceeded the norm. Since you can't ask the baby if its their tummy hurting, I guess you could have both, but how would you know ?