Low energy levels can be a sign of common dieting disasters.
One is skipping breakfast. Missing the first meal of the day not only allows muscle breakdown to go unchecked but also makes blood sugar levels fall. This can lead to huge lulls in available energy while also increasing the risk of binge eating. Another is eating low carb - 150grams or fewer per day, for too long. Try carb cycling, two days low and two days moderate. This will help drop fat, but you will also stay sane.