If you are exhausted after a reasonable workout, you probably need to do a better job on step 3 (find out what nutrients you are missing).
Or you're fucking fat(lol, by this I mean out of shape), and need to workout more. The more you workout, the less you are physically tired after, and the less you're sore the next day (or three if you are really out of shape). Then again, I could still be exhausted after doing something ridiculous, but it has to be something I don't do often.