Rochelle, my first thoughts were that is may be because of your diet recently - junk food etc. Your body may be recovering from that. I know i've been bad the last few days and i'm feeling tired and lethargic too, normally i've got stacks of energy.
Give it a few more days and if you don't pick up soon then it might be something to do with the shakes?? Do you get to eat any solids and if so how much? Could be your body adjusting to the shakes?
Just a few ideas - hope you feel better soon hun!
Saying goodbye to calorie counting AND scales for a while.
Just enjoying the new and improved healthy me and embracing my new lifestyle!