i don't think you have hit a plateau, the closer you get to your goal weight the harder it will be, sorry.
plus don't beat yourself up to bad, i feel the same way, i hate when my energy is down, it's horrible. i go through a lot of days like that, i am diabetic, so when my sugar is high i and down and out.
don't worry you will find it within yourself to do what you should do it. you have answered it yourself, it's your energy. remember it's okay to take a day off sometimes.