I have trouble with exhaustion too.  I have a 3 year old, so if I am tired I don't always have the option of sleep.  Usually when I'm exhausted I have to work really hard to stay away from the sugary stuff.  
A lot of my exhaustion is due to over-stimulation (noise, excitement, demands of my attention, etc.).  Since starting No-S, I have come to realize that my first response to being overwhelmed, tired, stressed is to eat food, when what I really need to do is get away from the noise and rest my brain (not always easy with a 3 year old).  I didn't always turn to food for this, but I think changing circumstances made eating food the easier option than my old ways of coping (I used to be skinny too 

 ).  Unfortunately, now it is a well established habit for me to crave food.  It's getting better though.  
Most of my after work habits were more like trained responses (like Pavlov's dogs haha).  Finish work - get a pastry (and a Coke- my worst vice).  I do not work at the same job anymore, but I still crave pastries every time I pass a certain establishment (usually after long and/or stressful shopping). It's hard to explain, but the combination of the route + the sight of the building + that cloudy headed feeling I get after work or long shopping with a crazy toddler = doughnut.  Luckily, they don't sell the kind I like anymore or I know I would have stopped a lot more often.
Anyway, these are my experiences with exhaustion and food.  I am trying to be more aware of any underlying cause of my exhaustion and it has really helped.  I am also trying to be more aware of my habits with food and drink to try to understand why I go overboard with certain things (like coffee).  The realization of the over-stimulation factor has been the biggest help for me.