Aching, creaking body

My back is killing me today, and my entire body hurt when I did my yoga this morning. I think it's because I did day 1 of week 8 in "Moving Toward Balance: Yoga in 8 weeks with Rodney yee" last night. The last week of the book contains much more intense workouts than previous weeks. That's a good thing for me, since I think I'm ready to move past the basics of the previous 7 weeks. Still, I can't deny that my entire body aches and creaks. Even the very act of raising my arms from standing forward bend to standing backbend hurts :P