What Causes Fatigue And Drowsiness In New Born?

My granddaughter was born five days ago, she scored high on apcor, her reflexes are good , but she is lethargic and being fed with breast milk, formula from a bottle and feeding tube through her nose...she is still in hospital, and sleeps mostly, she had a thyroid test, it was negative she ha an EEG but we haven t heard results yet, my daughter was genetically tested an d was negative for all diseases and syndromes.....she was 6 lbs 4 pounces when he was born, was Caesarian delivery but water broke two and a half days before, but she had no strong labor pains, baby was monitored whole time, my daughter wanted a vaginal delivery...that s why it took so long