Why do I keep waking up at 6 am??

It's so frustrating I went to bed at 11 pm and I woke up today at 5:53 even though I was planning to sleep until my son wakes up which is at 9 to 10 am, but instead I lost three valuable hours of sleep, I need my beauty sleep and my husband always says sleep when the baby sleeps but what do I do when my body clock keeps waking me up at 6 am???? Now I have to be awake till 11 pm because napping is very hard for me.