I've eaten out more than I've worked out in the last month
Why have you eaten out so much recently?
I just felt like eating out, you know? And if I eat out, then I've no  energy left.
It's fine to eat out sometimes, but you shouldn't eat poorly too often if you want to stay healthy. It's also important to exercise, so if what your eating is affecting your energy to work out, then you should change your habits.
Should I go on a diet?
Dieting is fine, eat more healthy foods. But you also want to make sure you do some exercizing on a regular basic to make sure your body moves around more too.