I think that a dramatic reduction in your intake of carbs in combination with more exercise than you’re used to could be making you feel crappy.
I try keep down the amount of carbs in my diet unless around exercise – i.e. before, during or after exercise when I make sure that I do take on some carbs (and protein e.g. milk, meat etc).
Not sure about processed sugars – not good for you and do turn to fat is my opinion.