Sometimes I feel very weak, distinct lack of energy, etc generally tired at work, I eat a candy bar and I feel better, is this related to diabetes or?

Unlikely. But if the habit is continued, can cause diabetes...Perhaps try to slowly cut down on candy bar towards healhier snack (ex. Mix candy with trail mix and slowly dilute out the candy, then dilute out glazed or salted nuts until you're eating plain nuts- much healthier). Be sure to eat healthy breakfast (high protein cereal like kashi go lean).
May be hunger. Weakness and lack of energy are common symptoms of hunger or low blood sugar in anyone, not just diabetics. Eating more healthy snacks high in protein can help tide you over for longer between meals.