Feeding

So my little bitty girl is 12 days old! She really struggles waking up for her feedings. Especially at night!! I always set an alarm for 3 hours but sometimes we let her go 4 because she doesnt wake up. Its staring to make me nervous. We go back to the Dr on tuesday, hopefully we can double check on everything too. She does eat really good during the day, the problem is only at nighth. If anyone has any advice or in the same situaution please help a mom out!!!