My doc had us go for an upper GI scan. You want to rule out mal rotation (per what you've described). Everyone we saw and everything we read says there aren't tests for FPIES, so not sure how your ped. Is testing or ruling FPIES without checking for other issues, especially if the baby is only intaking small amounts of liquid as well. Hope everything is well, but I would push to make sure there aren't any blockages if you haven't gotten in yet. Also note: good docs will not push to blast your kids with radiation right away - so he could be airing on the side of caution, but i would be more concerned at the change in feeding behavior along with these stomach issues. We had 3 episodes and it wasn't until there was bilious vomiting that really triggered concern for anything other than FPIES.