breast milk thinning out?

Caryn
I have had really thick breastmilk. My dr said most breastmilk is 20 calories but she thinks mine is 35. This is a good thing she said. Recently I've noticed it's a thinner consistency when I pump. Why is this? does this mean it has less calories? I've also noticed my daughter is only nursing for 5-8 minutes then falling asleep. Is she gettin. Enough?