Question without getting too personal - Our eldest was born a month early and was 5 pounds, 4 ounces at birth. At the week checkup, her body temperature was only 97 and she spent the weekend at the hospital. We heard the same phrasing as you've mentioned. Thing is, wife was trying to breastfeed but that wasn't working. As new parents without a clue, well...it's good that week checkups were/are a thing. We switched to formula and never had the issue again with the following three. Just something to think about.