Change in daily activity question

Hi all,

I'm a full time Mum to 3 boys and a midwifery student and my usual day consists of looking after kids, household chores, shopping, taxi driver, study and a 45 - 60 min workout.

The past 10 days I have been on placement - so working 8.5 hour shifts a day, half on my feet, half seated. Not getting all the workouts in but have tried to get a minimum of 30 mins per day (i.e. Ripped in 30). I am getting less sleep with 7am starts at work and I am exhausted. My question is whether I am tired due to lack of sleep and learning (why does that wear you out so much??) or whether I'm actually burning a different amount of calories each day? I feel less active, but don't know why I'm quite so worn out.

Any ideas?