Breast Milk Jaundice: This condition is common in breastfed babies, typically presenting in the first or second week of life. The total bilirubin level of 4.1 mg/dL with a direct bilirubin of 0.9 mg/dL is consistent with this diagnosis, as breast milk jaundice usually causes indirect hyperbilirubinemia.

Physiological Jaundice: This is a common condition in newborns, peaking around the 3rd to 5th day of life but can persist. The levels provided could still be within the range for physiological jaundice, especially if the baby is otherwise healthy.
Early Onset Breastfeeding Failure: In some cases, inadequate breastfeeding can lead to dehydration and exacerbate jaundice. The direct bilirubin level is slightly elevated, which might suggest some degree of hepatic or biliary involvement, but in the context of breastfeeding, this could also be related to early issues with milk intake.

Biliary Atresia: Although less likely given the age and the pattern of bilirubin elevation, biliary atresia is a critical diagnosis not to miss due to its severe consequences if left untreated. The slight elevation in direct bilirubin warrants consideration of this diagnosis.
Infections (e.g., Urinary Tract Infections, Sepsis): Infections can cause or exacerbate jaundice in newborns. While the bilirubin levels provided do not strongly suggest an infectious cause, the possibility should be considered, especially if other symptoms are present.
Hemolytic Disease of the Newborn (HDN): Although less common with modern prenatal screening, HDN can cause significant jaundice. The indirect bilirubin level is elevated, which could be consistent with hemolysis, but other signs and the direct bilirubin level do not strongly support this diagnosis without additional context.

Galactosemia: A rare genetic disorder that affects the body's ability to metabolize galactose, a sugar found in milk. It can cause jaundice, among other symptoms, but is less likely given the pattern of bilirubin elevation and the absence of other specific symptoms.
Congenital Hepatic Disorders (e.g., Alagille Syndrome): These are rare genetic disorders affecting the liver and can cause jaundice. The slight elevation in direct bilirubin might prompt consideration of these conditions, but they are less likely and would typically be associated with other findings.