Seems like you're doing a pretty good job, as darth vader said the body's reaction to a reduction in incoming food is to store up some more calories so just keep going, the other thing I'd say is that varying things as much as possible, eat plenty of fruit, and drink loads of cold water. Your tiredness might also stem from lowering your calorie intake. Ironically excerise is a great way to keep your body awake, once you get into a routine you'll find yourself energy levels increasing.