I haven't been exhausted, but I just got done with marathon training program before starting meso 1 and I feel more relaxed now doing this type of workout. Marathon training program is exhausting. I ran all those miles and did not lose, but now with these program I lost 5 pounds within the first three weeks.
Hopefully your body will adjust. Watch what you eat, such as enough protein. I found out that I wasn't getting enough and adding more along in the day helps. I have done a detox from sugar/carbs. I found out that I would eat theses, then crash shortly leaving me feeling horrilbe. I do have some type of sugar, but not as much as usual.
Good luck and happy lifting. I love STS.