So, week 2 down, and I'm exhausted

Man! This week (my "week" starts on Saturday) was rough. P90X only happened 4 times and I didn't even have tests, yet I'm wasted. But, I'm at 160 lbs. and 10% body fat (according to my scale, which could be off 5% or so easily). My goal is by the time I graduate dental school to be 175 lbs. and between 8-10% body fat. We'll see how I do.