My Newborn Grandson Born On 3/25 Had Jaundice With Levels

my newborn grandson born on 3/25 had jaundice with levels getting up to 19, but was hospitalized due to malrotation 1 week later with immediate surgery. Still in the hospital recovering and had been under the bilirubin light in the hospital, but levels had dropped down to 9.5, so no more light. They tested him today (2-3 days later) and it's back up to 12.? Is it unusual for bilirubin to fluctuate like that? Could it have been exacerbated by the surgery and inability to eat until just yesterday (starting with breast milk)?