Is My Baby Getting Enough?

My baby is 7 weeks olds and until a few days ago was breastfeeding (from what I could tell) very well but now I feel like all of the sudden she is falling asleep while nursing within a few minutes, I don't hear her taking big gulps as much and she doesn't seem to want to nurse long. Now this only really has been during the day, at night I can hear her gulping.

During the day I feed her every 2 hours, at night it's more like every 3-4. Should I wait longer during the day to feed her? Am I over worrying?

I plan on calling her Doctor Monday morning but wanted to see if anyone else experienced the same thing.