Ursofalk cancellation and jaundice return

Hello! My son, a month and a half. Recently, he lay in a hospital with the main diagnosis of prolonged conjugation jaundice. Bilirubin was 191, after 2 weeks at discharge it was 60. The treatment consisted mainly in my lactose-free diet and in the evenings - ursofalk. Upon returning home, I followed an equally rigid diet without taking Ursofalk. A week later, yellowness reappeared on the face. Since yesterday, I transferred it to nutrilon, for 4 days, I think. I do not understand what is the reason for the return of the jaundice I heard that modern babies often have intolerance to breast milk, or it is simply too heavy, and for this, mothers will be prescribed certain pills that can continue to breastfeed. What tests need to be done to understand whether there is a problem in my breastfeeding or not? Thank you in advance!