Bilirubin Level High in New Born.

My baby is born preterm ( 35 weeks 4 days) and he is 18 days old now.At the time of birth,his bilirubin Level is around 13.8. So the doctor suggested we give phototherapy treatment and we discharged at 10.8 level.After 5 days of discharge his bilirubin Level reached around 16.7 again and we admitted again and gave phototherapy treatment for 2 days and discharged again at 10.5 level...Now he is 18 days old and we are afraid whether we will give him the treatment again and again due to fluctuations of bilirubin Level...Baby is perfectly fine physically,he is drinking mother milk and passing urine and sometimes discharge yellow urine and stools.The question is will we have to test for bilirubin level again and again.Till what level is acceptable without admitting to hospital again for the radiation treatment??? Thank you