How low have you cut your cals to? Someone with your weight should be eating around 1500 cals. Also as electrongirl suggested are you eating from all food groups?
Lack of energy usually comes when you blood sugar levels stops peaking, so if you eat low GI foods you shouldn't experience lack of energy.
Maybe take some multi vitamins too
Start weight - 77kgs
Goal weight - 53kgs
Current Weight - 50.1kgs
No more weighing, no more scales. My measurement is my success at health. It's an investment I make every single day. My priority: be healthy!